[MAINT/TEST] Clarified conditions for setting IPTOS/TTL options. Added UT for this.

[ethouris]

Fixes #3095

Changes: maintained correctly and more clearly conditions for setting IP options on the UDP socket. Prevented the "ignored" case.

Added error logs that describe the problem, should one occur.

Added test that checks if setting these options.

[ethouris]

Problem on Mac so far:

191: [T/S] Bind @566589933 to: ::ffff:127.0.0.1:5001 (IPv6)
191: 16:54:43.584199/*E:SRT.km: setsockopt(IP_TTL): Invalid argument (v6 mapped v4)
191: [T/S] ... result -1 (expected to succeed)

To be investiaged.

On Windows probably should be disabled, although investigation would be in order, too:

189: [T/S] Bind @246382028 to: ::1:5000 (IPv6)
189: 16:57:00.489000/T1676*E:SRT.km: setsockopt(IPV6_TCLASS): An unknown, invalid, or unsupported option or level was specified in a getsockopt or setsockopt call.
189: 
189: [T/S] ... result -1 (expected to succeed)
189: D:\a\srt\srt\test\test_reuseaddr.cpp(267): error: Expected: (bind_res) != (SRT_ERROR), actual: -1 vs -1
189: [T/S] Bind @246382027 to: ::ffff:127.0.0.1:5001 (IPv6)
189: [T/S] ... result -1 (expected to succeed)
189: D:\a\srt\srt\test\test_reuseaddr.cpp(267): error: Expected: (bind_res) != (SRT_ERROR), actual: -1 vs -1