Fix Apple ECN dual stack behavior

[martinduke]

Commit Message: Check the status of ECN in a DualStack socket
Additional Description: Linux dual-stack sockets require IP_PROTO, IP_RECVTOS due to report ECN on incoming v4 sockets. Apple returns an error; IPV6_RECVTCLASS is sufficient for both IP versions.
Risk Level: Low
Testing: New unit tests to verify the sockopt is set, and ECN is reported on dual stack sockets
Docs Changes: N/A
Release Notes: N/A
Platform Specific Features: N/A

[KBaichoo]

Test failure is a known flake that we're working on. @danzh2010 does this look good to you?

[danzh2010]

Test failure is a known flake that we're working on. @danzh2010 does this look good to you?

I think this PR need more comments. I don't know how to mark resolved review comment unresolved.

[KBaichoo]

marked the comment unresolved

/wait

[yanavlasov]

@martinduke CI is stuck and I can not get it unstuck. Can you merge main to restart CI, please?

[soulxu]

/wait for a merge main

[soulxu]

@martinduke it seems you need to fix the DCO

[RyanTheOptimist]

/wait
@martinduke it looks like your PR has a problem with DCO that you need to fix

[martinduke]

/retest

[martinduke]

Marking ready for review, not because it's ready for review, but in the hope that this triggers the skipped iOS tests.

[RyanTheOptimist]

/wait

[martinduke]

/retest

[abeyad]

/retest

[martinduke]

Thanks to @abeyad, we were able to confirm this works correctly for Apple. Modulo the weird CI failures (apparently unrelated to the PR?) this is ready for review, and ultimately merge.

[RyanTheOptimist]

Thanks for getting to the bottom of this!

[RyanTheOptimist]

Can you update the PR description to make clear that this PR includes a behavior change, not just a new test?