RELENG_5 kernel b0rken with IPFIREWALL and without PFIL_HOOKS

Hi,

After recent changes I am unable to compile RELENG_5 kernel (and 
probably HEAD as well, but I have not tested it) with IPFIREWALL but 
without PFIL_HOOKS. Neither manpage, nor NOTES lists PFIL_HOOKS as a 
requirement for IPFIREWALL. Please fix.

-Maxim

cc -c -O -pipe -march=pentium4 -Wall -Wredundant-decls -Wnested-externs 
-Wstrict-prototypes  -Wmissing-prototypes -Wpointer-arith -Winline 
-Wcast-qual  -fformat-extensions -std=c99 -g -nostdinc -I-  -I. 
-I/voicelog/devel/src/sys -I/voicelog/devel/src/sys/contrib/dev/acpica 
-I/voicelog/devel/src/sys/contrib/altq 
-I/voicelog/devel/src/sys/contrib/ipfilter 
-I/voicelog/devel/src/sys/contrib/pf 
-I/voicelog/devel/src/sys/contrib/dev/ath 
-I/voicelog/devel/src/sys/contrib/dev/ath/freebsd 
-I/voicelog/devel/src/sys/contrib/ngatm -D_KERNEL -include opt_global.h 
-fno-common -finline-limit=8000 --param inline-unit-growth=100 --param 
large-function-growth=1000  -mno-align-long-strings 
-mpreferred-stack-boundary=2 -ffreestanding -Werror  vers.c
linking kernel.debug
ip_fw_pfil.o(.text+0x2ff): In function `ipfw_hook':
/voicelog/devel/src/sys/netinet/ip_fw_pfil.c:327: undefined reference to 
`pfil_head_get'
ip_fw_pfil.o(.text+0x32a):/voicelog/devel/src/sys/netinet/ip_fw_pfil.c:331: 
undefined reference to `pfil_add_hook'
ip_fw_pfil.o(.text+0x34a):/voicelog/devel/src/sys/netinet/ip_fw_pfil.c:332: 
undefined reference to `pfil_add_hook'
ip_fw_pfil.o(.text+0x37e): In function `ipfw_unhook':
/voicelog/devel/src/sys/netinet/ip_fw_pfil.c:345: undefined reference to 
`pfil_head_get'
ip_fw_pfil.o(.text+0x3a9):/voicelog/devel/src/sys/netinet/ip_fw_pfil.c:349: 
undefined reference to `pfil_remove_hook'
ip_fw_pfil.o(.text+0x3c9):/voicelog/devel/src/sys/netinet/ip_fw_pfil.c:350: 
undefined reference to `pfil_remove_hook'
*** Error code 1

Stop in /voicelog/devel/obj/voicelog/devel/src/sys/PBXPRESS.
*** Error code 1

Stop in /voicelog/devel/src.
*** Error code 1

Stop in /voicelog/devel/src.