selftests: mptcp: add mptcp_lib_wait_local_port_listen

commit 9369777c upstream.

To avoid duplicated code in different MPTCP selftests, we can add
and use helpers defined in mptcp_lib.sh.

wait_local_port_listen() helper is defined in diag.sh, mptcp_connect.sh,
mptcp_join.sh and simult_flows.sh, export it into mptcp_lib.sh and
rename it with mptcp_lib_ prefix. Use this new helper in all these
scripts.

Note: We only have IPv4 connections in this helper, not looking at IPv6
(tcp6) but that's OK because we only have IPv4 connections here in diag.sh.

Reviewed-by: Matthieu Baerts <matttbe@kernel.org>
Signed-off-by: Geliang Tang <geliang.tang@suse.com>
Signed-off-by: Mat Martineau <martineau@kernel.org>
Link: https://lore.kernel.org/r/20231128-send-net-next-2023107-v4-15-8d6b94150f6b@kernel.org


Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Stable-dep-of: 5afca7e9 ("selftests: mptcp: join: test for prohibited MPC to port-based endp")
[ Conflict in diag.sh, because commit 1f24ba67 ("selftests: mptcp:
  diag: check CURRESTAB counters") that is more recent that the one
  here, has been backported in this kernel version before, introducing
  chk_msk_cestab() helper in the same context. wait_local_port_listen()
  was still the same as in the original, and can then be simply removed
  from diag.sh. ]
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>