netfilter: core: add missing __rcu annotation

removes following sparse error:
net/netfilter/core.c:598:30: warning: incorrect type in argument 1 (different address spaces)
net/netfilter/core.c:598:30:    expected struct nf_hook_entries **e
net/netfilter/core.c:598:30:    got struct nf_hook_entries [noderef] <asn:4>**<noident>

Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/core.c

@@ -585,7 +585,8 @@ void (*nf_nat_decode_session_hook)(struct sk_buff *, struct flowi *);
 EXPORT_SYMBOL(nf_nat_decode_session_hook);
 #endif
 
-static void __net_init __netfilter_net_init(struct nf_hook_entries **e, int max)
+static void __net_init
+__netfilter_net_init(struct nf_hook_entries __rcu **e, int max)
 {
 	int h;