BUG/MINOR: contrib/prometheus-exporter: Respect the reserve when data are sent

The previous commit e6cdfe574 ("BUG/MINOR: contrib/prometheus-exporter: Don't
use channel_htx_recv_max()") is buggy. The buffer's reserve must be respected.

This patch must be backported to 2.0 and 1.9.

(cherry picked from commit 11921e6819a07219e8ed6adbdd276bdbdcdb324d)
Signed-off-by: Christopher Faulet <cfaulet@haproxy.com>
1 file changed