Merge branch 'mptcp-more-selftest-coverage-and-code-cleanup-for-net-next'

Mat Martineau says:

====================
mptcp: More selftest coverage and code cleanup for net-next

Patches 1-5 and 7-8 add selftest coverage (and an associated subflow
counter in the kernel) to validate the recently-updated handling of
subflows with ID 0.

Patch 6 renames a label in the userspace path manager for clarity.

Patches 9-11 and 13-15 factor out common selftest code by moving certain
functions to mptcp_lib.sh

Patch 12 makes sure the random data file generated for selftest
payloads has the intended size.

v3: https://lore.kernel.org/r/20231115-send-net-next-2023107-v3-0-1ef58145a882@kernel.org
v2: https://lore.kernel.org/r/20231114-send-net-next-2023107-v2-0-b650a477362c@kernel.org
v1: https://lore.kernel.org/r/20231027-send-net-next-2023107-v1-0-03eff9452957@kernel.org
====================

Link: https://lore.kernel.org/r/20231128-send-net-next-2023107-v4-0-8d6b94150f6b@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>