Merge branch 'follow-up-on-deduplicate-cookie-logic'

Willem de Bruijn says:

====================
follow-up on deduplicate cookie logic

1/3: I came across a leftover from cookie deduplication, due to UDP
having two code paths: lockless fast path and locked cork path.

3/3: Even though the leftover was in the fast path, this prompted me
to complete coverage to the cork path.

2/3: That uncovered a subtle API inconsistency in how dontfrag is
configured. It should not be possible to switch DF mid datagram.
====================

Link: https://patch.msgid.link/20250307033620.411611-1-willemdebruijn.kernel@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>