selftests/landlock: Test that MPTCP actions are not restricted

Extend protocol fixture with test suits for MPTCP protocol.
Add CONFIG_MPTCP and CONFIG_MPTCP_IPV6 options in config.

Signed-off-by: Mikhail Ivanov <ivanov.mikhail1@huawei-partners.com>
Link: https://lore.kernel.org/r/20250205093651.1424339-4-ivanov.mikhail1@huawei-partners.com


Cc: <stable@vger.kernel.org> # 6.7.x
Signed-off-by: Mickaël Salaün <mic@digikod.net>