selftests: mptcp: add the net device name testcase

This patch added a new testcase for setting the net device name. In it,
pass the net device name to pm_nl_ctl to set the ifindex field of struct
mptcp_pm_addr_entry.
Signed-off-by: Geliang Tang <geliangtang@gmail.com>
Signed-off-by: Mat Martineau <mathew.j.martineau@linux.intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

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

@@ -777,6 +777,14 @@ subflows_tests()
 	ip netns exec $ns2 ./pm_nl_ctl add 10.0.2.2 flags subflow
 	run_tests $ns1 $ns2 10.0.1.1
 	chk_join_nr "multiple subflows, limited by server" 2 2 1
+
+	# single subflow, dev
+	reset
+	ip netns exec $ns1 ./pm_nl_ctl limits 0 1
+	ip netns exec $ns2 ./pm_nl_ctl limits 0 1
+	ip netns exec $ns2 ./pm_nl_ctl add 10.0.3.2 flags subflow dev ns2eth3
+	run_tests $ns1 $ns2 10.0.1.1
+	chk_join_nr "single subflow, dev" 1 1 1
 }
 
 signal_address_tests()