BUG/MEDIUM: http-ana: Don't wait to send 1xx responses received from servers

When an informational response (1xx) is received, we must be sure to send it
ASAP. To do so, CF_SEND_DONTWAIT flag must be set on the response channel to
instruct the stream-interface to not set the CO_SFL_MSG_MORE flag on the
transport layer. Otherwise the response delivery may be delayed, because of the
commit 8945bb6c0 ("BUG/MEDIUM: stream-int: fix loss of CO_SFL_MSG_MORE flag in
forwarding").

Note that a previous patch (cf6898cd ["BUG/MINOR: http-ana: Don't wait to send
1xx responses generated by HAProxy"]) add this flag on 1xx responses generated
by HAProxy but not on responses coming from servers.

This patch must be backported to 2.2 and may be backported as far as 1.9, for
HTX part only. But this part has changed in the 2.2, so it may be a bit
tricky. Note it does not fix any known bug on 2.1 and below because the
CO_SFL_MSG_MORE flag is ignored by the h1 mux.

(cherry picked from commit 7d518454bb501659e8b13f38c22d216f5485be34)
Signed-off-by: Christopher Faulet <cfaulet@haproxy.com>
(cherry picked from commit 4777db423493d10cb97607b601c8ba9821b9a149)
Signed-off-by: Willy Tarreau <w@1wt.eu>
(cherry picked from commit 4ac4fb89da4fa2e54d680db1f73e37c4bfc07a29)
Signed-off-by: Amaury Denoyelle <adenoyelle@haproxy.com>
diff --git a/src/proto_htx.c b/src/proto_htx.c
index 35925c4..011a179 100644
--- a/src/proto_htx.c
+++ b/src/proto_htx.c
@@ -1729,6 +1729,7 @@
 		msg->flags = 0;
 		txn->status = 0;
 		s->logs.t_data = -1; /* was not a response yet */
+		rep->flags |= CF_SEND_DONTWAIT; /* Send ASAP informational messages */
 		goto next_one;
 	}