net/libpfctl: update main version

FreeBSD main has renamed PF_RT_RPOOL to PF_RT_RPOOL_RDR. Update libpfctl to cope
with this.
Stable branches never had this code, so are not updated.

Reported by: Olivier Cochard-Labbé <olivier@freebsd.org>
Sponsored by: Rubicon Communications, LLC ("Netgate")