CI fails on FreeBSD 15 for TCP_MAXPEAKRATE

CI is currently failing on FreeBSD 15 because TCP_MAXPEAKRATE is unknown.  That's because it was recently removed by this commit:
https://github.com/freebsd/freebsd-src/commit/87fbd9fc7fc5f8d79fe5e3dcd13ad02b11a67ef0 .  That, and other constants removed by the same commit, should be removed from libc's main branch and deprecated in the libc-0.2 branch.