Use C-style comments, not C++ style

apps/udpecho/udpecho.c

@@ -60,7 +60,7 @@ udpecho_thread(void *arg)
     if (err == ERR_OK) {
       addr = netbuf_fromaddr(buf);
       port = netbuf_fromport(buf);
-      // no need netconn_connect here, since the netbuf contains the address
+      /*  no need netconn_connect here, since the netbuf contains the address */
       if(netbuf_copy(buf, buffer, buf->p->tot_len) != buf->p->tot_len) {
         LWIP_DEBUGF(LWIP_DBG_ON, ("netbuf_copy failed\n"));
       } else {