Merge branch 'mptcp-misc-fixes-for-v6-17-rc'

Matthieu Baerts says:

====================
mptcp: misc fixes for v6.17-rc

Here are various fixes:

- Patch 1: Better handling SKB extension allocation failures.
  A fix for v5.7.

- Patches 2, 3: Avoid resetting MPTCP limits when flushing MPTCP
  endpoints. With a validation in the selftests. Fixes for v5.7.

- Patches 4, 5, 6: Disallow '0' as ADD_ADDR retransmission timeout.
  With a preparation patch, and a validation in the selftests.
  Fixes for v5.11.

- Patches 8, 9: Fix C23 extension warnings in the selftests,
  spotted by GCC. Fixes for v6.16.
====================

Link: https://patch.msgid.link/20250815-net-mptcp-misc-fixes-6-17-rc2-v1-0-521fe9957892@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>