Merge branch 'mptcp-some-clean-up-patches'

Matthieu Baerts says:

====================
mptcp: some clean-up patches

Here are some clean-up patches for MPTCP:

- Patch 1 drops duplicated header inclusions.

- Patch 2 updates PM 'set_flags' interface, to make it more similar to
  others.

- Patch 3 adds some error messages for the PM 'set_flags' command to
  help the userspace understanding what's wrong in case of error.

- Patch 4 simplifies __lookup_addr() function from pm_netlink.c.

Except for the 3rd patch, the behaviour is not supposed to be modified.
====================

Link: https://lore.kernel.org/r/20240305-upstream-net-next-20240304-mptcp-misc-cleanup-v1-0-c436ba5e569b@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>