Honor the SecRuleEngine while filtering connections

The SecRuleEngine has the capability to Enable, Disable or even to place the
ModSecurity in DetectionOnly mode. The SecReadStateLimit and SecWriteStateLimit
were not honoring such state, due the fact that our configuration belongs to
requests not to connections, the only struct that exists while those filters
are placed. By adding a global variable "conn_limits_filter_state" we are now
able to identify the current state of the ModSecurity, once the configuration
is loaded this variable is set and used by the connections filters.