pfctl: fix killing states by ID

Since the conversion to the new DIOCKILLSTATESNV the kernel no longer
exists the id and creatorid to be big-endian.
As a result killing states by id (i.e. pfctl -k id -k 12345) no longer
worked.

Reported by: Özkan KIRIK
MFC after: 1 week
Sponsored by: Rubicon Communications, LLC ("Netgate")