BUG/MINOR: h1-htx: Don't flag response as bodyless when a tunnel is established

BUG/MINOR: h1-htx: Don't flag response as bodyless when a tunnel is established

This reverts commit 225a4d02e1f6a12c0b4f3584949fad3339d71708.

When a 200-OK response is replied to a CONNECT request or a
101-Switching-protocol, a tunnel is considered as established between the
client and the server. However, we must not declare the reponse as
bodyless. Of course, there is no payload, but tunneled data are expected.

Because of this bug, the zero-copy forwarding is disabled on the server
side.

This patch must be backported as far as 2.9.

(cherry picked from commit a99d58819f8184fb6f500807ddaf2371c5f1c110)
Signed-off-by: Willy Tarreau <w@1wt.eu>