Actually here are the errors:

test# make
making sure the compat library is up to date...
`libcompat.a' is up to date.
making sure the kern library is up to date...
`libkern.a' is up to date.
#      link  PF/netbsd
ld -T ../../../../arch/mips/conf/kern.ldscript -Ttext 0x80001000 -e 
start -G 0 -x -o netbsd ${SYSTEM_OBJ} ${EXTRA_OBJ} vers.o
pf_ioctl.o(.text+0x4888): In function `pf_pfil_attach':
: undefined reference to `if_pfil'
pf_ioctl.o(.text+0x488c): In function `pf_pfil_attach':
: undefined reference to `if_pfil'
pf_ioctl.o(.text+0x4890): In function `pf_pfil_attach':
: undefined reference to `pfil_add_hook'
pf_ioctl.o(.text+0x48ac): In function `pf_pfil_attach':
: undefined reference to `if_pfil'
pf_ioctl.o(.text+0x48b0): In function `pf_pfil_attach':
: undefined reference to `if_pfil'
pf_ioctl.o(.text+0x48b4): In function `pf_pfil_attach':
: undefined reference to `pfil_add_hook'
pf_ioctl.o(.text+0x48c8): In function `pf_pfil_attach':
: undefined reference to `pfil_head_get'
pf_ioctl.o(.text+0x48e8): In function `pf_pfil_attach':
: undefined reference to `pfil_add_hook'
pf_ioctl.o(.text+0x4974): In function `pf_pfil_attach':
: undefined reference to `if_pfil'
pf_ioctl.o(.text+0x4978): In function `pf_pfil_attach':
: undefined reference to `if_pfil'
pf_ioctl.o(.text+0x497c): In function `pf_pfil_attach':
: undefined reference to `pfil_remove_hook'
pf_ioctl.o(.text+0x4990): In function `pf_pfil_attach':
: undefined reference to `if_pfil'
pf_ioctl.o(.text+0x4994): In function `pf_pfil_attach':
: undefined reference to `if_pfil'
pf_ioctl.o(.text+0x4998): In function `pf_pfil_attach':
: undefined reference to `pfil_remove_hook'
pf_ioctl.o(.text+0x4a0c): In function `pf_pfil_detach':
: undefined reference to `if_pfil'
pf_ioctl.o(.text+0x4a10): In function `pf_pfil_detach':
: undefined reference to `if_pfil'
pf_ioctl.o(.text+0x4a14): In function `pf_pfil_detach':
: undefined reference to `pfil_remove_hook'
pf_ioctl.o(.text+0x4a28): In function `pf_pfil_detach':
: undefined reference to `if_pfil'
pf_ioctl.o(.text+0x4a2c): In function `pf_pfil_detach':
: undefined reference to `if_pfil'
pf_ioctl.o(.text+0x4a30): In function `pf_pfil_detach':
: undefined reference to `pfil_remove_hook'
pf_ioctl.o(.text+0x4a3c): In function `pf_pfil_detach':
: undefined reference to `pfil_head_get'
pf_ioctl.o(.text+0x4a58): In function `pf_pfil_detach':
: undefined reference to `pfil_remove_hook'
*** Error code 1

Stop.
make: stopped in /usr/src/sys/arch/cobalt/compile/PF
test#