mwan3: don't try to use ipv6 if not installed

fix issue  #11826

Signed-off-by: Aaron Goodman <aaronjg@stanford.edu>
(cherry picked from commit a0d66d4eeb)

net/mwan3/files/usr/sbin/mwan3

@@ -90,6 +90,7 @@ policies()
 	echo "Current ipv4 policies:"
 	mwan3_report_policies_v4
 	echo -e
+	[ $NO_IPV6 -ne 0 ] && return
 	echo "Current ipv6 policies:"
 	mwan3_report_policies_v6
 	echo -e
@@ -100,6 +101,7 @@ connected()
 	echo "Directly connected ipv4 networks:"
 	mwan3_report_connected_v4
 	echo -e
+	[ $NO_IPV6 -ne 0 ] && return
 	echo "Directly connected ipv6 networks:"
 	mwan3_report_connected_v6
 	echo -e
@@ -110,6 +112,7 @@ rules()
 	echo "Active ipv4 user rules:"
 	mwan3_report_rules_v4
 	echo -e
+	[ $NO_IPV6 -ne 0 ] && return
 	echo "Active ipv6 user rules:"
 	mwan3_report_rules_v6
 	echo -e
@@ -161,7 +164,7 @@ stop()
 	config_foreach mwan3_track_clean interface
 
 	for IP in "$IP4" "$IP6"; do
-
+		[ "$IP" = "$IP6" ] && [ $NO_IPV6 -ne 0 ] && continue
 		for route in $(seq 1 $MWAN3_INTERFACE_MAX); do
 			$IP route flush table $route &> /dev/null
 		done
@@ -172,7 +175,7 @@ stop()
 	done
 
 	for IPT in "$IPT4" "$IPT6"; do
-
+		[ "$IPT" = "$IPT6" ] && [ $NO_IPV6 -ne 0 ] && continue
 		$IPT -D PREROUTING -j mwan3_hook &> /dev/null
 		$IPT -D OUTPUT -j mwan3_hook &> /dev/null