selftests: mptcp: add MPC backup tests

Add a couple of test-cases covering the newly introduced
features - priority update for the MPC subflow.

Reviewed-by: Mat Martineau <mathew.j.martineau@linux.intel.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Mat Martineau <mathew.j.martineau@linux.intel.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

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

@@ -2428,6 +2428,36 @@ backup_tests()
 		chk_add_nr 1 1
 		chk_prio_nr 1 1
 	fi
+
+	if reset "mpc backup"; then
+		pm_nl_add_endpoint $ns2 10.0.1.2 flags subflow,backup
+		run_tests $ns1 $ns2 10.0.1.1 0 0 0 slow
+		chk_join_nr 0 0 0
+		chk_prio_nr 0 1
+	fi
+
+	if reset "mpc backup both sides"; then
+		pm_nl_add_endpoint $ns1 10.0.1.1 flags subflow,backup
+		pm_nl_add_endpoint $ns2 10.0.1.2 flags subflow,backup
+		run_tests $ns1 $ns2 10.0.1.1 0 0 0 slow
+		chk_join_nr 0 0 0
+		chk_prio_nr 1 1
+	fi
+
+	if reset "mpc switch to backup"; then
+		pm_nl_add_endpoint $ns2 10.0.1.2 flags subflow
+		run_tests $ns1 $ns2 10.0.1.1 0 0 0 slow backup
+		chk_join_nr 0 0 0
+		chk_prio_nr 0 1
+	fi
+
+	if reset "mpc switch to backup both sides"; then
+		pm_nl_add_endpoint $ns1 10.0.1.1 flags subflow
+		pm_nl_add_endpoint $ns2 10.0.1.2 flags subflow
+		run_tests $ns1 $ns2 10.0.1.1 0 0 0 slow backup
+		chk_join_nr 0 0 0
+		chk_prio_nr 1 1
+	fi
 }
 
 add_addr_ports_tests()