MINOR: http-act: mark http-request access control actions with KWF_ACCESS_CTRL

MINOR: http-act: mark http-request access control actions with KWF_ACCESS_CTRL

This new keyword flag indicates that an action is used to block traffic,
and as such that the reliability of its condition matters. It is set on
the "deny", "tarpit", "reject", "auth" and "silent-drop" http-request
actions. It will be used to detect such rules relying on a deny-list of
aliasable contents. "return" is deliberately not marked, as it's used
for many other purposes (e.g. serving local contents).