Merge branch 'mptcp-refactoring-for-one-selftest-and-csum-validation'

Mat Martineau says:

====================
mptcp: Refactoring for one selftest and csum validation

Patch 1 changes the MPTCP join self tests to depend more on events
rather than delays, so the script runs faster and has more consistent
results.

Patches 2 and 3 get rid of some duplicate code in MPTCP's checksum
validation by modifying and leveraging an existing helper function.
====================

Link: https://lore.kernel.org/r/20220107192524.445137-1-mathew.j.martineau@linux.intel.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>