Merge branch 'mptcp-fix-fallback-mib-counter-and-wrong-var-in-selftests'

Matthieu Baerts says:

====================
mptcp: fix fallback MIB counter and wrong var in selftests

Here are two fixes related to MPTCP.

The first patch fixes when the MPTcpExtMPCapableFallbackACK MIB counter
is modified: it should only be incremented when a connection was using
MPTCP options, but then a fallback to TCP has been done. This patch also
checks the counter is not incremented by mistake during the connect
selftests. This counter was wrongly incremented since its introduction
in v5.7.

The second patch fixes a wrong parsing of the 'dev' endpoint options in
the selftests: the wrong variable was used. This option was not used
before, but it is going to be soon. This issue is visible since v5.18.
====================

Link: https://lore.kernel.org/r/20240329-upstream-net-20240329-fallback-mib-v1-0-324a8981da48@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>