Update FRR to recent stable release

[sysvinit]

Due to recurring problems with FRR since we upgraded most of our hardware from 21.05 to 24.11, we've decided to update our pinned FRR version from 8.5.7 to the much more recent 10.1.2. Nixpkgs stable currently only has 10.1, and this has some bugs in the handling of IPv4-via-IPv6 nexthops which render it unsuitable for our use case, so this change retains our version pinning with the newer version.

I've additionally refactored the RIB integrity check script to use the new JSON interface of the bridge command (new since 21.05) to improve the robustness of the script, and I've written an additional FRR test with a (very simple) sanity check for working MAC mobility functionality.

@flyingcircusio/release-managers

Release process

• Created changelog entry using ./changelog.sh => none, internal change.

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)
  • Software version update.
  • Refactoring tools for changing interfaces of third party software.
• Security requirements tested? (EVIDENCE)
  • The Hydra tests are clean.
  • Manually tested on a development host.
  • We're relying on our development and staging environments in order to test the new FRR version under real workloads, as this requires greater scale and resources than we have in the integration test environment.