libpfctl: fix pfctl_kill_states()

735748f30a changed the output of the states so that the creator id
endianness would be consistent. This means that we need to convert the
host endianness creatorid back to big-endian before we give it to the
kernel.

MFC after: 3 weeks
Sponsored by: Rubicon Communications, LLC ("Netgate")

(cherry picked from commit 6f47a72d8ebf444641bda192b33eb217c9013811)