nat_traversal: use dedicated function for testing via address against source ip

(cherry picked from commit c6c4230fb0c4ca18f5c681c7195d3e1531255f3a)

modules/nat_traversal/nat_traversal.c

@@ -820,7 +820,7 @@ test_source_address(struct sip_msg *msg)
     Bool different_ip, different_port;
     int via1_port;
 
-    different_ip = received_test(msg);
+    different_ip = received_via_test(msg);
     via1_port = (msg->via1->port ? msg->via1->port : SIP_PORT);
     different_port = (msg->rcv.src_port != via1_port);