selftests: mptcp: join: simplify deny_join_id0_tests

The six join id0 tests can be divided into three groups in sequence,
with two tests in each one. Both tests in one group are similar, only
different namespaces used. So a for-loop can be used to simplify these
tests.

Signed-off-by: Geliang Tang <geliang.tang@suse.com>

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

@@ -2896,27 +2896,20 @@ deny_join_id0_tests()
 		chk_join_nr 0 0 0
 	fi
 
-	# signal address allow join id0 ns1
+	# signal address allow join id0 ns1/2
 	# ADD_ADDRs are not affected by allow_join_id0 value.
-	if reset_with_allow_join_id0 "signal address allow join id0 ns1" 1 0; then
-		pm_nl_set_limits $ns1 1 1
-		pm_nl_set_limits $ns2 1 1
-		pm_nl_add_endpoint $ns1 10.0.2.1 flags signal
-		run_tests $ns1 $ns2 10.0.1.1
-		chk_join_nr 1 1 1
-		chk_add_nr 1 1
-	fi
-
-	# signal address allow join id0 ns2
-	# ADD_ADDRs are not affected by allow_join_id0 value.
-	if reset_with_allow_join_id0 "signal address allow join id0 ns2" 0 1; then
-		pm_nl_set_limits $ns1 1 1
-		pm_nl_set_limits $ns2 1 1
-		pm_nl_add_endpoint $ns1 10.0.2.1 flags signal
-		run_tests $ns1 $ns2 10.0.1.1
-		chk_join_nr 1 1 1
-		chk_add_nr 1 1
-	fi
+	local ns enable="1 0"
+	for ns in "ns1" "ns2"; do
+		[ $ns == "ns2" ] && enable="0 1"
+		if reset_with_allow_join_id0 "signal address allow join id0 $ns" $enable; then
+			pm_nl_set_limits $ns1 1 1
+			pm_nl_set_limits $ns2 1 1
+			pm_nl_add_endpoint $ns1 10.0.2.1 flags signal
+			run_tests $ns1 $ns2 10.0.1.1
+			chk_join_nr 1 1 1
+			chk_add_nr 1 1
+		fi
+	done
 
 	# subflow and address allow join id0 ns1
 	if reset_with_allow_join_id0 "subflow and address allow join id0 1" 1 0; then