WITHOUT_PF breaks buildworld

From: Gary Jennejohn <gljennjohn_at_gmail.com>
Date: Sun, 19 Dec 2021 10:47:23 UTC
Some recent change, probably in a .mk file, breaks builworld on HEAD
when WITHOUT_PF is enabled in src.conf.

Disabling WITHOUT_PF results in a successful buildworld.

The reported error is that netpfil/pf/pf.h can't be found.

-- 
Gary Jennejohn