http: fix backport of Slowloris headers

The backport of 618eebdd17 was
not complete, and the starting time to parse the headers was not reset.

PR-URL: #24796
Fixes: #24760
Reviewed-By: Rod Vagg <rod@vagg.org>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>

Author: mcollina

lib/_http_server.js

@@ -481,6 +481,9 @@ function connectionListener(socket) {
   function parserOnIncoming(req, shouldKeepAlive) {
     incoming.push(req);
 
+    // Set to zero to communicate that we have finished parsing.
+    socket.parser.parsingHeadersStart = 0;
+
     // If the writable end isn't consuming, then stop reading
     // so that we don't become overwhelmed by a flood of
     // pipelined requests that may never be resolved.