BUG/MINOR: http: don't log a 503 on client errors while waiting for requests

If a client aborts a request with an error (typically a TCP reset), we must
log a 400. Till now we did not set the status nor close the stream interface,
causing the request to attempt to be forwarded and logging a 503.

Should be backported to 1.4 which is affected as well.
diff --git a/src/proto_http.c b/src/proto_http.c
index 0e51c08..54850d7 100644
--- a/src/proto_http.c
+++ b/src/proto_http.c
@@ -2334,6 +2334,8 @@
 				session_inc_http_err_ctr(s);
 			}
 
+			txn->status = 400;
+			stream_int_retnclose(req->prod, NULL);
 			msg->msg_state = HTTP_MSG_ERROR;
 			req->analysers = 0;