BUG/MINOR: http-ana: Don't increment HTTP error counter on internal errors

BUG/MINOR: http-ana: Don't increment HTTP error counter on internal errors

If internal error is reported by the mux during HTTP request parsing, the
HTTP error counter should not be incremented. It should only be incremented
on parsing error to reflect errors caused by clients.

This patch must be backported as far as 2.0. During the backport, the same
must be performed for 408-request-time-out errors.

(cherry picked from commit bf7175f9b6480fa25e859e226a1f460744e163cd)
Signed-off-by: Christopher Faulet <cfaulet@haproxy.com>