Don't depend on the ip module - FreeBSD doesn't have one.
Use an mbuf as the third argument to the ip probes. This way we can
provide that argument both stacks - the struct ip * is only available in
the IPv4 stack.
More work on the ip provider:

- Add probes in the IPv4 forwarding fastpath.
- Add IPv6 probes.
- Add protocol strings.
Merge branch '20130324-clean-ports-modules' into 20130421-ip-provider
Fix ipinfo_t translation in the IPv4 case.
Fix argument extraction for probes with more than 5 arguments.
Merge branch 'markj-kernel-config' into 20130421-ip-provider
Merge branch '20130421-ip-provider' into markj-develop