Merge branch 'mptcp-pm-drop-tcp-ts-with-add_addrv6-port'

Matthieu Baerts says:

====================
mptcp: pm: drop TCP TS with ADD_ADDRv6 + port

Up to this series, it was possible to add a "signal" MPTCP endpoint with
an IPv6 address and a port, or to directly request to send an ADD_ADDR
with a v6 address and a port, but the expected ADD_ADDR wasn't sent when
TCP timestamps was used for the connection.

In fact, such signalling option cannot be sent when TCP timestamps is
used due to a lack of option space: the limit is at 40 bytes, and, with
padding, TCP timestamps is taking 12 bytes, while an ADD_ADDR IPv6 +
port is taking 30 bytes. The selected solution here is to simply drop
the TCP timestamps option when such ADD_ADDR of 30 bytes needs to be
sent.

- Patches 1-3: small cleanups to avoid computing ADD/RM_ADDR twice.

- Patches 4-7: the new feature, controlled by a new sysctl knob.

- Patch 8: extra checks in the MPTCP Join selftests.

- Patches 9-15: A bunch of refactoring: renamed confusing helpers and
  variables, and prevent future misused functions.
====================

Link: https://patch.msgid.link/20260605-net-next-mptcp-add-addr6-port-ts-v2-0-758e7ca73f4d@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>