Merge branch 'mptcp-pm-special-case-for-c-flag-luminar-endp'

Merge branch 'mptcp-pm-special-case-for-c-flag-luminar-endp'

Matthieu Baerts says:

====================
mptcp: pm: special case for c-flag + luminar endp

Here are some patches for the MPTCP PM, including some refactoring that
I thought it would be best to send at the end of a cycle to avoid
conflicts between net and net-next that could last a few weeks.

The most interesting changes are in the first and last patch, the rest
are patches refactoring the code & tests to validate the modifications.

- Patches 1 & 2: When servers set the C-flag in their MP_CAPABLE to tell
  clients not to create subflows to the initial address and port -- e.g.
  a deployment behind a L4 load balancer like a typical CDN deployment
  -- clients will not use their other endpoints when default settings
  are used. That's because the in-kernel path-manager uses the 'subflow'
  endpoints to create subflows only to the initial address and port. The
  first patch fixes that (for >=v5.14), and the second one validates it.

- Patches 3-14: various patches refactoring the code around the
  in-kernel PM (mainly): split too long functions, rename variables and
  functions to avoid confusions, reduce structure size, and compare IDs
  instead of IP addresses. Note that one patch modifies one internal
  variable used in one BPF selftest.

- Patch 15: ability to control endpoints that are used in reaction to a
  new address announced by the other peer. With that, endpoints can be
  used only once.
====================

Link: https://patch.msgid.link/20250925-net-next-mptcp-c-flag-laminar-v1-0-ad126cc47c6b@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>