v2.1: quic: disable send fairness (backport of #4586)

[mergify]

Problem

quinn-rs/quinn#2002 was implemented in Quinn but never activated in Agave.

Summary of Changes

Disable send fairness in Quic (transport config).

---

This is an automatic backport of pull request #4586 done by Mergify.

[mergify]

Cherry-pick of 1e721f0 has failed:

On branch mergify/bp/v2.1/pr-4586
Your branch is up to date with 'origin/v2.1'.

You are currently cherry-picking commit 1e721f086.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	modified:   sdk/src/quic.rs

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   quic-client/src/nonblocking/quic_client.rs
	both modified:   streamer/src/nonblocking/testing_utilities.rs
	both modified:   tpu-client-next/src/quic_networking.rs

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally