[NETFILTER]: net/ipv[46]/netfilter.c cleanups

Don't wrap entire file in #ifdef CONFIG_NETFILTER, remove a few
unneccessary includes.

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/netfilter_ipv6.h

@@ -72,7 +72,12 @@ enum nf_ip6_hook_priorities {
 	NF_IP6_PRI_LAST = INT_MAX,
 };
 
+#ifdef CONFIG_NETFILTER
 extern int ipv6_netfilter_init(void);
 extern void ipv6_netfilter_fini(void);
+#else /* CONFIG_NETFILTER */
+static inline int ipv6_netfilter_init(void) { return 0; }
+static inline void ipv6_netfilter_fini(void) { return; }
+#endif /* CONFIG_NETFILTER */
 
 #endif /*__LINUX_IP6_NETFILTER_H*/