BUG/MEDIUM: http: properly retrieve the front connection

Commit 350f487 ("CLEANUP: session: simplify references to chn_{prod,cons}(&s->{req,res})")
introduced a regression causing the cli_conn to be picked from the server
side instead of the client side, so the XFF header is not appended anymore
since the connection is NULL.

Thanks to Reinis Rozitis for reporting this bug. No backport is needed
as it's 1.6-specific.
1 file changed