Updated handler_i_am_add to also display the responder's MAC

(IP) address when PRINT_ENABLED is defined. This will help 
when debugging duplicate BACNET IDs in a multi-device 
configuration.

bacnet-stack/demo/handler/h_iam.c

@@ -52,7 +52,9 @@ void handler_i_am_add(
 #endif
     if (len != -1) {
 #if PRINT_ENABLED
-        fprintf(stderr, " from %u!\n", device_id);
+      fprintf(stderr, " from %u, MAC = %d.%d.%d.%d.%d.%d\n",device_id,
+            src->mac[0],src->mac[1],src->mac[2],
+            src->mac[3],src->mac[4],src->mac[5]);
 #endif
         address_add(device_id, max_apdu, src);
     } else {