Merge branch 'tcp-re-enable-acceptance-of-fin-packets-when-rwin-is-0'

Simon Baatz says:

====================
tcp: re-enable acceptance of FIN packets when RWIN is 0

this series restores the ability to accept in‑sequence FIN packets
even when the advertised receive window is zero, and adds a
packetdrill test to guard the behavior.
====================

Link: https://patch.msgid.link/20260224-fix_zero_wnd_fin-v2-0-a16677ea7cea@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>