after quick search in google:
I will test to patch latest linux kernel with pf.
Hey! Wait: "The name of this patchset is not connected with BSD Packet Filter. «pf» means «post-factum» in the short form."
What do you thing?
Get OpenBSD. Honestly -- all the porting stuff of relatively kernel-close stuff is just braindead.
If you need PF, get OpenBSD.