sip-router-oob.cfg: user src_ip instead of @src.ip

Using the built-in src_ip is slightly faster then the @src.ip
select and also more consistent with the other src_ip checks in
the config.

etc/sip-router-oob.cfg

@@ -1166,7 +1166,7 @@ route[AUTHENTICATION]
 	# You have to trust them base on some other information such as the
 	# source IP address.
 	# WARNING: If at all this is only safe in a local network!
-	if (@src.ip == $gw_ip) {
+	if (src_ip == $gw_ip) {
 		break;
 	}
 
@@ -1298,7 +1298,7 @@ route[INBOUND]
 		# clause in the next line and closing bracket below.
 		# WARNING: If at all you should trust IP addresses only in
 		#          your local network!
-		#if (@src.ip == $gw_ip) {
+		#if (src_ip == $gw_ip) {
 			route(SESSION_TIMER);
 		#}