net: fallback to IPv6-only when dual-stack bind fails

[suii2210]

Summary

When IPv4 is unavailable, Node.js may fail while creating the default IPv6 dual-stack listening socket. Setting IPV6_V6ONLY=0 can return EAFNOSUPPORT, after which the existing code falls back to IPv4, which is also unavailable.

This change retries the IPv6 bind with UV_TCP_IPV6ONLY enabled before falling back to IPv4.

Tests

• Added test/sequential/test-net-server-listen-ipv6-only-system.js
• tools/test.py test/sequential/test-net-server-listen-ipv6-only-system.js
• make lint

Refs: #65400

[nodejs-github-bot]

Review requested:

• @nodejs/net

[MikeMcC399]

Please make sure you have read and understood the following documents:

• guide for first-time contributors
• contribution and automation policies
• pull request guide
• AI use policy
• Code of Conduct

The advice in the above documents says that you may use the Slack channel if your PR is not getting attention. That means you should be patient and wait. Posting to Slack 20 minutes after opening your PR is too fast by a long way.

[suii2210]

Please make sure you have read and understood the following documents:

• guide for first-time contributors
• contribution and automation policies
• pull request guide
• AI use policy
• Code of Conduct

The advice in the above documents says that you may use the Slack channel if your PR is not getting attention. That means you should be patient and wait. Posting to Slack 20 minutes after opening your PR is too fast by a long way.

I’m really sorry for the inconvenience 🥺. I’ll be more patient from now on and will make sure I don’t repeat this mistake again.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.04%. Comparing base (7aaf9b4) to head (4d6af84).
⚠️ Report is 83 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #65669      +/-   ##
==========================================
- Coverage   90.13%   90.04%   -0.10%     
==========================================
  Files         751      754       +3     
  Lines      253639   255761    +2122     
  Branches    47790    48328     +538     
==========================================
+ Hits       228618   230293    +1675     
- Misses      16264    16590     +326     
- Partials     8757     8878     +121     

Files with missing lines	Coverage Δ
lib/net.js	94.58% <100.00%> (+0.02%)	⬆️

... and 98 files with indirect coverage changes

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