selftests: mptcp: fix proto type in link_failure tests

In listener_ns, we should pass srv_proto argument to mptcp_connect command,
not cl_proto.

Fixes: 7d1e6f1639 ("selftests: mptcp: add testcase for active-back")
Signed-off-by: Geliang Tang <geliang.tang@suse.com>
Signed-off-by: Matthieu Baerts <matthieu.baerts@tessares.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

tools/testing/selftests/net/mptcp/mptcp_join.sh

@@ -297,7 +297,7 @@ do_transfer()
 	if [ "$test_link_fail" -eq 2 ];then
 		timeout ${timeout_test} \
 			ip netns exec ${listener_ns} \
-				$mptcp_connect -t ${timeout_poll} -l -p $port -s ${cl_proto} \
+				$mptcp_connect -t ${timeout_poll} -l -p $port -s ${srv_proto} \
 					${local_addr} < "$sinfail" > "$sout" &
 	else
 		timeout ${timeout_test} \