kernel - merge fixes from FreeBSD

kernel - merge fixes from FreeBSD

* Merge 8159278dbd8e019, fixes to pf_get_sport().  Primarily fixes the state
  key used to check whether a port is in-use or not.  NAT could previously
  choose a port that was already in-use.

* bzero() the state key to ensure that uninitialized fields are zero,
  otherwise the RB_FIND is likely to fail.

* Cleanup the case where there is no port range or the protocol is not
  supported.  In this situation, sport must be replicated on the host.