mptcp: rebase to 5.16 net-next

Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2028420 Tested: LNST, Tier1, self-tests and pktdrill

This rebases the MPTCP protocol to commit 59060a47ca50 ("mptcp: clean up harmless false expressions"), which is roughly 5.16 net-next.

It also includes a bunch of follow-up fixes and a few TCP pre-reqs. Note that TCP improvement touching the MPTCP protocol are intentionally omitted.

This series includes the skb cache usage removal, already present in rhel-8.5, which should land into rhel-9, too

Signed-off-by: Paolo Abeni pabeni@redhat.com