Merge branch 'tcp-rfc-7323-compliant-window-retraction-handling'

Simon Baatz says:

====================
tcp: RFC 7323-compliant window retraction handling

this series implements the receiver-side requirements for TCP window
retraction as specified in RFC 7323 and adds packetdrill tests to
cover the new behavior.

Please see the first patch for background and implementation
details. Since MPTCP adjusts the TCP receive window on subflows, the
relevant MPTCP code paths are updated accordingly.
====================

Link: https://patch.msgid.link/20260309-tcp_rfc7323_retract_wnd_rfc-v3-0-4c7f96b1ec69@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>