move kernel ipfw-related sources to a separate directory,

adjust conf/files and modules' Makefiles accordingly.

No code or ABI changes so this and most of previous related
changes can be easily MFC'ed

MFC after:	5 days

sys/conf/files

@@ -2334,14 +2334,14 @@ netinet/in_proto.c		optional inet \
 	compile-with "${NORMAL_C} -I$S/contrib/pf"
 netinet/in_rmx.c		optional inet
 netinet/ip_divert.c		optional ipdivert
-netinet/ip_dummynet.c		optional dummynet
+netinet/ipfw/ip_dummynet.c	optional dummynet
 netinet/ip_ecn.c		optional inet | inet6
 netinet/ip_encap.c		optional inet | inet6
 netinet/ip_fastfwd.c		optional inet
-netinet/ip_fw2.c		optional ipfirewall \
+netinet/ipfw/ip_fw2.c		optional ipfirewall \
 	compile-with "${NORMAL_C} -I$S/contrib/pf"
-netinet/ip_fw_pfil.c		optional ipfirewall
-netinet/ip_fw_nat.c		optional ipfirewall_nat
+netinet/ipfw/ip_fw_pfil.c	optional ipfirewall
+netinet/ipfw/ip_fw_nat.c	optional ipfirewall_nat
 netinet/ip_icmp.c		optional inet
 netinet/ip_input.c		optional inet
 netinet/ip_ipsec.c		optional ipsec

sys/modules/dummynet/Makefile

@@ -2,7 +2,7 @@
 
 .include <bsd.own.mk>
 
-.PATH:  ${.CURDIR}/../../netinet
+.PATH:  ${.CURDIR}/../../netinet/ipfw
 KMOD=   dummynet
 SRCS=   ip_dummynet.c
 SRCS+=	opt_inet6.h

sys/modules/ipfw/Makefile

@@ -2,7 +2,7 @@
 
 .include <bsd.own.mk>
 
-.PATH: ${.CURDIR}/../../netinet
+.PATH: ${.CURDIR}/../../netinet/ipfw
 
 KMOD=	ipfw
 SRCS=	ip_fw2.c ip_fw_pfil.c

sys/modules/ipfw_nat/Makefile

@@ -1,6 +1,6 @@
 # $FreeBSD$
 
-.PATH: ${.CURDIR}/../../netinet
+.PATH: ${.CURDIR}/../../netinet/ipfw
 
 KMOD=   ipfw_nat
 SRCS=   ip_fw_nat.c