Merge branch 'mptcp-various-rare-sending-issues'

Matthieu Baerts says:

====================
mptcp: various rare sending issues

Here are various fixes from Paolo, addressing very occasional issues on
the sending side:

- Patch 1: drop an optimisation that could lead to timeout in case of
  race conditions. A fix for up to v5.11.

- Patch 2: fix stream corruption under very specific conditions.
  A fix for up to v5.13.

- Patch 3: restore MPTCP-level zero window probe after a recent fix.
  A fix for up to v5.16.

- Patch 4: new MIB counter to track MPTCP-level zero windows probe to
  help catching issues similar to the one fixed by the previous patch.
====================

Link: https://patch.msgid.link/20251028-net-mptcp-send-timeout-v1-0-38ffff5a9ec8@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>