pfctl: Fix printing af-to "to" pool

We can't depend on pool->cur, that is used only inside of kernel for
iterating over members of the pool, it is not filled in during loading
of ruleset.

Reviewed by: kp
Approved by: kp (mentor)
Sponsored by: InnoGames GmbH
Differential Revision: https://reviews.freebsd.org/D49213