Merge branch 'mptcp-misc-minor-cleanups'

Matthieu Baerts says:

====================
mptcp: misc minor cleanups

Here are some small unrelated cleanups collected when working on some
fixes recently.

- Patches 1 & 2: close file descriptors in exit paths in the selftests.

- Patch 3: fix a wrong type (int i/o u32) when parsing netlink message.
====================

Link: https://patch.msgid.link/20250912-net-next-mptcp-minor-fixes-6-18-v1-0-99d179b483ad@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>