mwan3: reduce unnecessary comparisons

Signed-off-by: David Yang <mmyangfl@gmail.com>

net/mwan3/files/lib/mwan3/mwan3.sh

@@ -203,9 +203,7 @@ mwan3_create_iface_iptables()
 	[ -n "$id" ] || return 0
 
 	if [ "$family" == "ipv4" ]; then
-
-		ubus call network.interface.${1}_4 status &>/dev/null
-		if [ "$?" -eq "0" ]; then
+		if ubus call network.interface.${1}_4 status &>/dev/null; then
 			network_get_ipaddr src_ip ${1}_4
 		else
 			network_get_ipaddr src_ip $1
@@ -244,9 +242,7 @@ mwan3_create_iface_iptables()
 	fi
 
 	if [ "$family" == "ipv6" ]; then
-
-		ubus call network.interface.${1}_6 status &>/dev/null
-		if [ "$?" -eq "0" ]; then
+		if ubus call network.interface.${1}_6 status &>/dev/null; then
 			network_get_ipaddr6 src_ipv6 ${1}_6
 		else
 			network_get_ipaddr6 src_ipv6 $1
@@ -322,8 +318,7 @@ mwan3_create_iface_route()
 	[ -n "$id" ] || return 0
 
 	if [ "$family" == "ipv4" ]; then
-		ubus call network.interface.${1}_4 status &>/dev/null
-		if [ "$?" -eq "0" ]; then
+		if ubus call network.interface.${1}_4 status &>/dev/null; then
 			network_get_gateway route_args ${1}_4
 		else
 			network_get_gateway route_args $1
@@ -336,9 +331,7 @@ mwan3_create_iface_route()
 	fi
 
 	if [ "$family" == "ipv6" ]; then
-
-		ubus call network.interface.${1}_6 status &>/dev/null
-		if [ "$?" -eq "0" ]; then
+		if ubus call network.interface.${1}_6 status &>/dev/null; then
 			network_get_gateway6 route_args ${1}_6
 		else
 			network_get_gateway6 route_args $1