Added MDNS and driver support for multicast

src/net_builtin.c

@@ -1129,6 +1129,10 @@ void mg_connect_resolved(struct mg_connection *c) {
 
 bool mg_open_listener(struct mg_connection *c, const char *url) {
   c->loc.port = mg_htons(mg_url_port(url));
+  if (!mg_aton(mg_url_host(url), &c->loc)) {
+    MG_ERROR(("invalid listening URL: %s", url));
+    return false;
+  }
   return true;
 }
 
@@ -1216,4 +1220,10 @@ bool mg_send(struct mg_connection *c, const void *buf, size_t len) {
   }
   return res;
 }
+
+#if MG_TCPIP_MCAST
+const uint8_t mcast_addr[6] = {0x01, 0x00, 0x5e, 0x00, 0x00, 0xfb};
+void mg_mcast_add(char *ip, MG_SOCKET_TYPE fd) { (void) ip; (void) fd; }
+#endif
+
 #endif  // MG_ENABLE_TCPIP