ipfw build error with WITHOUT_PF (pfvar.h)

Hi.

There is a problem in recent -current to build ipfw with WITHOUT_PF
option, introduced in r257215. altq.c file produce error due to included
<net/pfvar.h> have following includes

#include <netpfil/pf/pf.h>
#include <netpfil/pf/pf_altq.h>
#include <netpfil/pf/pf_mtag.h>

and netpfil/pf directory is empty in
/usr/src/include/Makefile with WITHOUT_PF option.