selftests: mptcp: check subflow and addr infos

New MPTCP info are being checked in multiple places to improve the code
coverage when using the userspace PM.

This patch makes chk_mptcp_info() more generic to be able to check
subflows, add_addr_signal and add_addr_accepted info (and even more
later). New arguments are now required to get different infos from the
two namespaces because some counters are specific to the client or the
server.

Reviewed-by: Matthieu Baerts <matthieu.baerts@tessares.net>
Signed-off-by: Geliang Tang <geliang.tang@suse.com>
Signed-off-by: Mat Martineau <martineau@kernel.org>
Link: https://lore.kernel.org/r/20230623-send-net-next-20230623-v1-2-a883213c8ba9@kernel.org


Signed-off-by: Jakub Kicinski <kuba@kernel.org>