This patch makes sure the kernel can be compiled with CONFIG_XFRM=y and
CONFIG_NETFILTER off.

--- linux-2.6.5/include/linux/netfilter_ipv4.h.dbg	2004-04-27 13:00:55.000000000 +0200
+++ linux-2.6.5/include/linux/netfilter_ipv4.h	2004-04-27 13:15:24.000000000 +0200
@@ -86,7 +86,7 @@
 extern int skb_ip_make_writable(struct sk_buff **pskb,
 				unsigned int writable_len);
 
-#ifdef CONFIG_XFRM
+#if defined(CONFIG_XFRM) && defined(CONFIG_NETFILTER)
 #include <net/route.h>
 #include <net/xfrm.h>