BUG/MINOR: http-ana: Don't eval front after-response rules if stopped on back

BUG/MINOR: http-ana: Don't eval front after-response rules if stopped on back

http-after-response rules evaluation must be stopped after a "allow". It
means the frontend ruleset must not be evaluated if a "allow" was performed
in the backend ruleset. Internally, the evaluation must be stopped if on
HTTP_RULE_RES_STOP return value. Only the "allow" action is concerned by
this change.

Thanks to this patch, http-response and http-after-response behave in the
same way.

This patch should be backported as far as 2.2.