coordinator: improve determining the default route for IPv6

[cyclinder]

For high kernels, netlink consolidates multiple default routes into the MultiPath field within a single route structure. However, for older kernels, each default route is represented by a separate Route structure.

Thanks for contributing!

What type of PR is this?

• release/bug

What this PR does / why we need it:

For high kernels, netlink consolidates multiple default routes into the MultiPath field within a single route structure. However, for older kernels, each default route is represented by a separate Route structure.

Which issue(s) this PR fixes:

Fixes #2917

Special notes for your reviewer:

[codecov]

Codecov Report

Merging #2919 (ef2fb32) into main (921f004) will not change coverage.
The diff coverage is n/a.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2919   +/-   ##
=======================================
  Coverage   81.15%   81.15%           
=======================================
  Files          49       49           
  Lines        5333     5333           
=======================================
  Hits         4328     4328           
  Misses        850      850           
  Partials      155      155           

Flag	Coverage Δ
unittests	81.15% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

[cyclinder]

• [FAILED] [0.255 seconds]
test ippool CR [BeforeEach] [ippoolCR]
/home/runner/work/spiderpool/spiderpool/test/e2e/ippoolcr/ippoolcr_test.go:33
  create and delete batch of ippool and check time cost [D00006]
  /home/runner/work/spiderpool/spiderpool/test/e2e/ippoolcr/ippoolcr_test.go:387

  Timeline >>
  > Enter [BeforeEach] test ippool CR - /home/runner/work/spiderpool/spiderpool/test/e2e/ippoolcr/ippoolcr_test.go:33 @ 12/15/23 04:11:24.188
  Subnet v4-ss-53f07ea2ff27ced overlaps with subnet v4-ss-1f868a4b502c987, the overlapping subnet is: 192.229.96.0/24 
  [FAILED] Unexpected error:
      <*errors.StatusError | 0xc00040f5e0>: 
      admission webhook "spidersubnet.spiderpool.spidernet.io" denied the request: SpiderSubnet.spiderpool.spidernet.io "v4-ss-53f07ea2ff27ced" is invalid: spec.subnet: Invalid value: "192.229.96.0/24": overlap with Subnet v4-ss-1f868a4b502c987 which 'spec.subnet' is 192.229.96.0/24
      {
          ErrStatus: {
              TypeMeta: {Kind: "", APIVersion: ""},
              ListMeta: {
                  SelfLink: "",
                  ResourceVersion: "",
                  Continue: "",
                  RemainingItemCount: nil,
              },
              Status: "Failure",
              Message: "admission webhook \"spidersubnet.spiderpool.spidernet.io\" denied the request: SpiderSubnet.spiderpool.spidernet.io \"v4-ss-53f07ea2ff27ced\" is invalid: spec.subnet: Invalid value: \"192.229.96.0/24\": overlap with Subnet v4-ss-1f868a4b502c987 which 'spec.subnet' is 192.229.96.0/24",
              Reason: "Invalid",
              Details: {
                  Name: "v4-ss-53f07ea2ff27ced",
                  Group: "spiderpool.spidernet.io",
                  Kind: "SpiderSubnet",
                  UID: "",
                  Causes: [
                      {
                          Type: "FieldValueInvalid",
                          Message: "Invalid value: \"192.229.96.0/24\": overlap with Subnet v4-ss-1f868a4b502c987 which 'spec.subnet' is 192.229.96.0/24",
                          Field: "spec.subnet",
                      },
                  ],
                  RetryAfterSeconds: 0,
              },
              Code: 422,
          },
      }
  occurred
  In [BeforeEach] at: /home/runner/work/spiderpool/spiderpool/test/e2e/ippoolcr/ippoolcr_test.go:38 @ 12/15/23 04:11:24.443
  < Exit [BeforeEach] test ippool CR - /home/runner/work/spiderpool/spiderpool/test/e2e/ippoolcr/ippoolcr_test.go:33 @ 12/15/23 04:11:24.443 (255ms)

[ty-dc]

• [FAILED] [0.255 seconds]
test ippool CR [BeforeEach] [ippoolCR]
/home/runner/work/spiderpool/spiderpool/test/e2e/ippoolcr/ippoolcr_test.go:33
  create and delete batch of ippool and check time cost [D00006]
  /home/runner/work/spiderpool/spiderpool/test/e2e/ippoolcr/ippoolcr_test.go:387

  Timeline >>
  > Enter [BeforeEach] test ippool CR - /home/runner/work/spiderpool/spiderpool/test/e2e/ippoolcr/ippoolcr_test.go:33 @ 12/15/23 04:11:24.188
  Subnet v4-ss-53f07ea2ff27ced overlaps with subnet v4-ss-1f868a4b502c987, the overlapping subnet is: 192.229.96.0/24 
  [FAILED] Unexpected error:
      <*errors.StatusError | 0xc00040f5e0>: 
      admission webhook "spidersubnet.spiderpool.spidernet.io" denied the request: SpiderSubnet.spiderpool.spidernet.io "v4-ss-53f07ea2ff27ced" is invalid: spec.subnet: Invalid value: "192.229.96.0/24": overlap with Subnet v4-ss-1f868a4b502c987 which 'spec.subnet' is 192.229.96.0/24
      {
          ErrStatus: {
              TypeMeta: {Kind: "", APIVersion: ""},
              ListMeta: {
                  SelfLink: "",
                  ResourceVersion: "",
                  Continue: "",
                  RemainingItemCount: nil,
              },
              Status: "Failure",
              Message: "admission webhook \"spidersubnet.spiderpool.spidernet.io\" denied the request: SpiderSubnet.spiderpool.spidernet.io \"v4-ss-53f07ea2ff27ced\" is invalid: spec.subnet: Invalid value: \"192.229.96.0/24\": overlap with Subnet v4-ss-1f868a4b502c987 which 'spec.subnet' is 192.229.96.0/24",
              Reason: "Invalid",
              Details: {
                  Name: "v4-ss-53f07ea2ff27ced",
                  Group: "spiderpool.spidernet.io",
                  Kind: "SpiderSubnet",
                  UID: "",
                  Causes: [
                      {
                          Type: "FieldValueInvalid",
                          Message: "Invalid value: \"192.229.96.0/24\": overlap with Subnet v4-ss-1f868a4b502c987 which 'spec.subnet' is 192.229.96.0/24",
                          Field: "spec.subnet",
                      },
                  ],
                  RetryAfterSeconds: 0,
              },
              Code: 422,
          },
      }
  occurred
  In [BeforeEach] at: /home/runner/work/spiderpool/spiderpool/test/e2e/ippoolcr/ippoolcr_test.go:38 @ 12/15/23 04:11:24.443
  < Exit [BeforeEach] test ippool CR - /home/runner/work/spiderpool/spiderpool/test/e2e/ippoolcr/ippoolcr_test.go:33 @ 12/15/23 04:11:24.443 (255ms)

Ah, this is a known issue and it's been happening more and more frequently lately. -_-!!!
Will be repaired soon.

It happens occasionally and helps you re-run CI