[BUG] http: fix computation of message body length after forwarding has started

Till now, the forwarding code was making use of the hdr_content_len member
to hold the size of the last chunk parsed. As such, it was reset after being
scheduled for forwarding. The issue is that this entry was reset before the
data could be viewed by backend.c in order to parse a POST body, so the
"balance url_param check_post" did not work anymore.

In order to fix this, we need two things :
  - the chunk size (reset upon every forward)
  - the total body size (not reset)

hdr_content_len was thus replaced by the former (hence the size of the patch)
as it makes more sense to have it stored that way than the way around.

This patch should be backported to 1.4 with care, considering that it affects
the forwarding code.
3 files changed