Merge branch 'mptcp-fixes-for-5-13'

Mat Martineau says:

====================
mptcp: Fixes for 5.13

These patches address two issues in MPTCP.

Patch 1 fixes a locking issue affecting MPTCP-level retransmissions.

Patches 2-4 improve handling of out-of-order packet arrival early
in a connection, so it falls back to TCP rather than forcing a
reset. Includes a selftest.
====================

Link: https://lore.kernel.org/r/20210527233140.182728-1-mathew.j.martineau@linux.intel.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>