MEDIUM: http: add support for "http-request tarpit" rule

MEDIUM: http: add support for "http-request tarpit" rule

The "reqtarpit" rule is not very handy to use. Now that we have more
flexibility with "http-request", let's finally make the tarpit rules
usable there.

There are still semantical differences between apply_filters_to_request()
and http_req_get_intercept_rule() because the former updates the counters
while the latter does not. So we currently have almost similar code leafs
for similar conditions, but this should be cleaned up later.