Merge branch 'mptcp-various-small-and-unrelated-improvements'

Matthieu Baerts says:

====================
mptcp: various small and unrelated improvements

Here are various unrelated patches:

- Patch 1: sched: remove unused structure.

- Patch 2: sched: split the validation part, a preparation for later.

- Patch 3: pm: clarify code, not to think there is a possible UaF.
  Note: a previous version has already been sent individually to Netdev.

- Patch 4: subflow: simplify subflow_hmac_valid by passing subflow_req.

- Patch 5: mib: add counter for MPJoin rejected by the PM.

- Patch 6: selftests: validate this new MPJoinRejected counter.

- Patch 7: selftests: define nlh variable only where needed.

- Patch 8: selftests: show how to use IPPROTO_MPTCP with getaddrinfo.
  Note: a previous version has already been sent individually to Netdev.

v1: https://lore.kernel.org/20250411-net-next-mptcp-sched-mib-sft-misc-v1-0-85ac8c6654c3@kernel.org
====================

Link: https://patch.msgid.link/20250413-net-next-mptcp-sched-mib-sft-misc-v2-0-0f83a4350150@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>