[NET]: Fix sparse warnings

Of this type, mostly:

CHECK   net/ipv6/netfilter.c
net/ipv6/netfilter.c:96:12: warning: symbol 'ipv6_netfilter_init' was not declared. Should it be static?
net/ipv6/netfilter.c:101:6: warning: symbol 'ipv6_netfilter_fini' was not declared. Should it be static?

Signed-off-by: Arnaldo Carvalho de Melo <acme@mandriva.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/linux/netfilter_ipv6.h b/include/linux/netfilter_ipv6.h
index 5d204ee..edcc2c6 100644
--- a/include/linux/netfilter_ipv6.h
+++ b/include/linux/netfilter_ipv6.h
@@ -71,7 +71,7 @@
 	NF_IP6_PRI_LAST = INT_MAX,
 };
 
-int ipv6_netfilter_init(void);
-void ipv6_netfilter_fini(void);
+extern int ipv6_netfilter_init(void);
+extern void ipv6_netfilter_fini(void);
 
 #endif /*__LINUX_IP6_NETFILTER_H*/