[PATCH] fix ip_conntrack_core.h compile error

From: Felipe Alfaro Solana <felipe_alfaro@linuxmail.org>

Fix compile error in 2.6.0-test2 when Netfilter IP connection tracking
is enabled.

include/linux/netfilter_ipv4/ip_conntrack_core.h

 #ifndef _IP_CONNTRACK_CORE_H
 #define _IP_CONNTRACK_CORE_H
+#include <linux/netfilter.h>
 #include <linux/netfilter_ipv4/lockhelp.h>
 
 /* This header is used to share core functionality between the