Merge branch 'mptcp-subflow-accounting-fix'

Mat Martineau says:

====================
mptcp: Subflow accounting fix

This series contains a bug fix affecting the in-kernel path manager
(patch 1), where closing subflows would sometimes not adjust the PM's
count of active subflows. Patch 2 updates the selftests to exercise the
new code.
====================

Link: https://lore.kernel.org/r/20220512232642.541301-1-mathew.j.martineau@linux.intel.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>