BUG/MEDIUM: http-client: Ask for more room when request data cannot be xferred

BUG/MEDIUM: http-client: Ask for more room when request data cannot be xferred

When the request payload cannot be xferred to the channel because its buffer
is full, we must request for more room by calling sc_need_room(). It is
important to be sure the httpclient applet will not be woken up in loop to
push more data while it is not possible.

It is only an issue with large POSTs, when the payload is streamed.

This patch must be backported as far as 2.6. Note that on 2.6,
sc_need_room() only takes one argument.

(cherry picked from commit e4a0d40c62594b4504fd7443158731fef54e040a)
Signed-off-by: Amaury Denoyelle <adenoyelle@haproxy.com>
(cherry picked from commit 5377ea587fba88b56e5249008be153cb529f066b)
Signed-off-by: Christopher Faulet <cfaulet@haproxy.com>