Move mg_mqtt_next-* to the example, and some nits

src/ws.c

@@ -272,6 +272,7 @@ void mg_ws_upgrade(struct mg_connection *c, struct mg_http_message *hm,
     ws_handshake(c, wskey, wsproto, fmt, &ap);
     va_end(ap);
     c->is_websocket = 1;
+    c->is_resp = 0;
     mg_call(c, MG_EV_WS_OPEN, hm);
   }
 }