sing-quic: Fix missing user context in packet connections #2276

Job	Run time
Debug build (Go 1.20)	1m 18s
Debug build	1m 4s
Debug build (Go 1.18)	1m 7s
cross (windows-amd64, windows, amd64, v1)	35s
cross (windows-amd64-v3, windows, amd64, v3)	48s
cross (windows-386, windows, 386)	42s
cross (windows-arm64, windows, arm64)	38s
cross (windows-arm32v7, windows, arm, 7)	35s
cross (linux-amd64, linux, amd64, v1)	48s
cross (linux-amd64-v3, linux, amd64, v3)	42s
cross (linux-386, linux, 386)	40s
cross (linux-arm64, linux, arm64)	45s
cross (linux-armv5, linux, arm, 5)	48s
cross (linux-armv6, linux, arm, 6)	46s
cross (linux-armv7, linux, arm, 7)	46s
cross (linux-mips-softfloat, linux, mips, softfloat)	35s
cross (linux-mips-hardfloat, linux, mips, hardfloat)	41s
cross (linux-mipsel-softfloat, linux, mipsle, softfloat)	36s
cross (linux-mipsel-hardfloat, linux, mipsle, hardfloat)	39s
cross (linux-mips64, linux, mips64)	44s
cross (linux-mips64el, linux, mips64le)	45s
cross (linux-s390x, linux, s390x)	34s
cross (darwin-amd64, darwin, amd64, v1)	44s
cross (darwin-amd64-v3, darwin, amd64, v3)	44s
cross (darwin-arm64, darwin, arm64)	45s
cross (freebsd-amd64, freebsd, amd64, v1)	46s
cross (freebsd-amd64-v3, freebsd, amd64, v3)	46s
cross (freebsd-386, freebsd, 386)	44s
cross (freebsd-arm64, freebsd, arm64)	45s
	21m 50s

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