#48 add a function to walk active configuration

[Darren]

rather than build walking of active filter rules into ipfstat, put it in libipf

[Darren]

This feature request will cover the following:
- filter rules
- ipnat rules
- hostmap table entries for nat
- active nat entries
- active state entries
... and in the short term, it will all just go into 6.0

[Darren]

this should cover all data that is used by ipfstat/ipnat, such as hostmap, nat table, nat rules, state table, firewall rules, groups