Fix socket race condition in port tracking

[chemwolf6922]

Summary of the Pull Request

This PR makes the bind 0 port resolution in port tracking inline. To avoid duplicating the socket and causing race conditions. With the trade off of even slower bind calls.

PR Checklist

• Closes: VSCode Remote-SSH SSH tunnel stuck on WSL2 2.7.1 #40109
• Communication: I've discussed this with core contributors already. If work hasn't been agreed, this work might be rejected
• Tests: Added/updated if needed and all pass
• Localization: All end user facing strings can be localized
• Dev docs: Added/updated if needed
• Documentation updated: If checked, please file a pull request on our docs repo and link it here: #xxx

Detailed Description of the Pull Request / Additional comments

#40178 would be a better but much more complex solution. Which may not be worth it if the seccomp part is still required.

Validation Steps Performed

The problem described in #40109 is reproduceable. I have validated that this PR will fix the issue.
NetworkTests::MirroredTests::PortZeroBindIsTracked [Passed]
NetworkTests::VirtioProxyTests::PortZeroBindIsTracked [Passed]

[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

This PR removes the background thread used to resolve port-0 (ephemeral) binds and instead resolves them inline in the main GnsPortTracker::Run() loop to avoid duplicating sockets and triggering race conditions.

Changes:

• Removed deferred port-0 resolution thread/queues and related synchronization primitives.
• Made ResolvePortZeroBind return std::optional<PortAllocation> and resolve/register port-0 binds synchronously.
• Simplified port-0 bind processing by directly calling HandleRequest/TrackPort after resolution.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
src/linux/init/GnsPortTracker.h	Removes deferred-resolution thread machinery; updates ResolvePortZeroBind signature to return an optional allocation.
src/linux/init/GnsPortTracker.cpp	Deletes deferred resolver thread/queues; resolves port-0 binds inline and registers allocations immediately.