Merge branch 'tcp-tcp-challenge-ack-fixes'

Eric Dumazet says:

====================
tcp: tcp challenge ack fixes

syzbot found a typical data-race addressed in the first patch.

While we are at it, second patch makes the global rate limit
per net-ns and disabled by default.
====================

Link: https://lore.kernel.org/r/20220830185656.268523-1-eric.dumazet@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>