libpfctl: fix creatorid endianness

We provide the hostid (which is the state creatorid) to the kernel as a
big endian number (see pfctl/pfctl.c pfctl_set_hostid()), so convert it
back to system endianness when we get it from the kernel.

This avoids a confusing mismatch between the value the user configures
and the value displayed in the state.

MFC after: 3 weeks
Sponsored by: Rubicon Communications, LLC ("Netgate")
Differential Revision: https://reviews.freebsd.org/D33989