Using wait for multiplexing over HTTP/1.x

When a large burst of DNS requests came in and the
only HTTPS/2 connection was too many time in idle state,
curl closes it and opens brand new connection for every
single DNS request.
Obviously later it will keep only 1 and close all the others.
So it is better to wait for multiplexing.
When testing this setting, the DNS query latency values
did not raise.

Author: baranyaib90

src/https_client.c

@@ -315,7 +315,7 @@ static void https_fetch_ctx_init(https_client_t *client,
   ASSERT_CURL_EASY_SETOPT(ctx, CURLOPT_WRITEFUNCTION, &write_buffer);
   ASSERT_CURL_EASY_SETOPT(ctx, CURLOPT_WRITEDATA, ctx);
   ASSERT_CURL_EASY_SETOPT(ctx, CURLOPT_MAXAGE_CONN, 300L);
-  // FIXME: consider adding CURLOPT_PIPEWAIT
+  ASSERT_CURL_EASY_SETOPT(ctx, CURLOPT_PIPEWAIT, client->opt->use_http_version > 1);
   ASSERT_CURL_EASY_SETOPT(ctx, CURLOPT_USERAGENT, "https_dns_proxy/0.3");
   ASSERT_CURL_EASY_SETOPT(ctx, CURLOPT_FOLLOWLOCATION, 0);
   ASSERT_CURL_EASY_SETOPT(ctx, CURLOPT_NOSIGNAL, 0);