Merge branch 'mptcp-various-small-improvements'

Matthieu Baerts says:

====================
mptcp: various small improvements

This series brings various small improvements to MPTCP and its
selftests:

Patch 1 prints an error if there are duplicated subtests names. It is
important to have unique (sub)tests names in TAP, because some CI
environments drop (sub)tests with duplicated names.

Patch 2 is a preparation for patches 3 and 4, which check the protocol
in tcp_sk() and mptcp_sk() with DEBUG_NET, only in code from net/mptcp/.
We recently had the case where an MPTCP socket was wrongly treated as a
TCP one, and fuzzers and static checkers never spot the issue. This
would prevent such issues in the future.

Patches 5 to 7 are some cleanup for the MPTCP selftests. These patches
are not supposed to change the behaviour.

Patch 8 sets the poll timeout in diag selftest to the same value as the
one used in the other selftests.
====================

Link: https://lore.kernel.org/r/20240223-upstream-net-next-20240223-misc-improvements-v1-0-b6c8a10396bd@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>