http_async_client: disable HTTP/2 multiplexing

src/modules/http_async_client/http_multi.c

@@ -402,6 +402,7 @@ int init_http_multi(struct event_base *evbase, struct http_m_global *wg)
 	curl_multi_setopt(g->multi, CURLMOPT_SOCKETDATA, g);
 	curl_multi_setopt(g->multi, CURLMOPT_TIMERFUNCTION, multi_timer_cb);
 	curl_multi_setopt(g->multi, CURLMOPT_TIMERDATA, g);
+	curl_multi_setopt(g->multi, CURLMOPT_PIPELINING, CURLPIPE_NOTHING);
 
 	return init_http_m_table(hash_size);
 }