Update channel to use downgraded kernel version.

[sysvinit]

In the most recent nixpkgs update #1039 we released kernel version 5.15.165, however this has a bug in the virtio_net driver which causes network performance problems in VMs.

I've created a feature branch on our nixpkgs fork with the update commit reverted; this change switches our nixpkgs channel to use that feature branch, so we can continue to use 5.15.164, which does not have this regression.

PL-132971

@flyingcircusio/release-managers

Release process

Impact:

• [NixOS 24.05] Machines will reboot to activate the downgraded kernel.

Changelog:

• linux_5_15: 5.15.165 -> 5.15.164

PR release workflow (internal)

• PR has internal ticket
• internal issue ID (PL-…) part of branch name
• internal issue ID mentioned in PR description text
• ticket is on Platform agile board
• ticket state set to Pull request ready
• if ticket is more urgent than within the next few days, directly contact a member of the Platform team

Design notes

• Provide a feature toggle if the change might need to be adjusted/reverted quickly depending on context. Consider whether the default should be on or off. Example: rate limiting.
• All customer-facing features and (NixOS) options need to be discoverable from documentation. Add or update relevant documentation such that hosted and guided customers can understand it as well.

Security implications

• Security requirements defined? (WHERE)
  • The most recently released new kernel version has a regression which may degrade service availability.
• Security requirements tested? (EVIDENCE)
  • Checked on a DEV VM with the reproduction test against RadosGW.