Merge branch 'clean-up-and-refactor-cookie_v46_check'

Kuniyuki Iwashima says:

====================
tcp: Clean up and refactor cookie_v[46]_check().

This is a preparation series for upcoming arbitrary SYN Cookie
support with BPF. [0]

There are slight differences between cookie_v[46]_check().  Such a
discrepancy caused an issue in the past, and BPF SYN Cookie support
will add more churn.

The primary purpose of this series is to clean up and refactor
cookie_v[46]_check() to minimise such discrepancies and make the
BPF series easier to review.

[0]: https://lore.kernel.org/netdev/20231121184245.69569-1-kuniyu@amazon.com/
v2: https://lore.kernel.org/netdev/20231125011638.72056-1-kuniyu@amazon.com/
v1: https://lore.kernel.org/netdev/20231123012521.62841-1-kuniyu@amazon.com/
====================

Link: https://lore.kernel.org/r/20231129022924.96156-1-kuniyu@amazon.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>