selftests: mptcp: join: check re-using ID of closed subflow

commit 65fb58afa341ad68e71e5c4d816b407e6a683a66 upstream.

This test extends "delete and re-add" to validate the previous commit. A
new 'subflow' endpoint is added, but the subflow request will be
rejected. The result is that no subflow will be established from this
address.

Later, the endpoint is removed and re-added after having cleared the
firewall rule. Before the previous commit, the client would not have
been able to create this new subflow.

While at it, extra checks have been added to validate the expected
numbers of MPJ and RM_ADDR.

The 'Fixes' tag here below is the same as the one from the previous
commit: this patch here is not fixing anything wrong in the selftests,
but it validates the previous fix for an issue introduced by this commit
ID.

Fixes: b6c08380

 ("mptcp: remove addr and subflow in PM netlink")
Cc: stable@vger.kernel.org
Reviewed-by: Mat Martineau <martineau@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Link: https://patch.msgid.link/20240819-net-mptcp-pm-reusing-id-v1-4-38035d40de5b@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
[ Conflicts in mptcp_join.sh, because this subtest has been modified in
  newer versions, e.g. commit 9095ce97 ("selftests: mptcp: add
  mptcp_info tests") added chk_mptcp_info check, commit 03668c65
  ("selftests: mptcp: join: rework detailed report") changed the way
  the info are displayed, commit 04b57c9e

 ("selftests: mptcp: join:
  stop transfer when check is done (part 2)") uses the new
  mptcp_lib_kill_wait helper instead of kill_tests_wait.
  Conflicts have been resolved by not using the new helpers, the rest
  was the same. ]
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>