Merge branch 'mptcp-prevent-mpc-handshake-on-port-based-signal-endpoints'

Matthieu Baerts says:

====================
mptcp: prevent MPC handshake on port-based signal endpoints

MPTCP connection requests toward a listening socket created by the
in-kernel PM for a port based signal endpoint will never be accepted,
they need to be explicitly rejected.

- Patch 1: Explicitly reject such requests. A fix for >= v5.12.

- Patch 2: Cover this case in the MPTCP selftests to avoid regressions.

Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
v1: https://lore.kernel.org/20240908180620.822579-1-xiyou.wangcong@gmail.com

Link: https://lore.kernel.org/a5289a0d-2557-40b8-9575-6f1a0bbf06e4@redhat.com
====================

Link: https://patch.msgid.link/20241014-net-mptcp-mpc-port-endp-v2-0-7faea8e6b6ae@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>