In FreeBSD each redirection pool (struct pf_kpool) consists of multiple
hosts (struct pf_addr_wrap). In OpenBSD that is not the case, and a
round-robin pool having a table as a host loops infinitely only over
that single table.

In FreeBSD once all addresses from a table are returned the pool must
iterate to the next host. Add a custom flag to have pfr_pool_get() break
its loop once it reaches the last index. Use this flag in round-robin
pools. When changing pool's host set index to 0 to always start
iterating each table from beginning.