The current API for adding rules with pool addresses is the following:

• DIOCADDADDR adds addresses and puts them into V_pf_pabuf
• DIOCADDRULE takes all addresses from V_pf_pabuf and links them into rule.

The ugly part is that if address is a table, then it is initialized
in DIOCADDRULE, because we need ruleset, and DIOCADDADDR doesn't
supply ruleset. But if address is a dynaddr, we need address family,
and address family could be different for different addresses in one
rule, so dynaddr is initialized in DIOCADDADDR.

This leads to the entangled state of addresses on V_pf_pabuf. Some are
initialized, and some not. That's why running pf_empty_pool(&V_pf_pabuf)
can lead to a panic on a NULL table address.

Since proper fix requires API/ABI change, for now simply plug the panic
in pf_empty_pool().

Reported by: danger