Add the kernel to the includes search path; ipf.c depends on it.

libexec/ftp-proxy/Makefile

@@ -1,4 +1,4 @@
-#	$NetBSD: Makefile,v 1.2 2004/06/30 13:29:43 darrenr Exp $
+#	$NetBSD: Makefile,v 1.3 2004/07/01 01:41:16 kleink Exp $
 #	$OpenBSD: Makefile,v 1.4 2003/11/20 23:23:09 avsm Exp $
 #	@(#)Makefile	8.2 (Berkeley) 4/4/94
 
@@ -8,6 +8,7 @@ MAN=	ftp-proxy.8
 
 WARNS?=	2
 
+CPPFLAGS+=-I${NETBSDSRCDIR}/sys
 CPPFLAGS+=-DLIBWRAP
 LDADD+=	-lwrap
 DPADD+=	${LIBWRAP}