net: make neigh_ops constant

These tables are never modified at runtime. Move to read-only
section.

Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/neighbour.h b/include/net/neighbour.h
index 18b69b6..3817fda 100644
--- a/include/net/neighbour.h
+++ b/include/net/neighbour.h
@@ -118,7 +118,7 @@
 	int			(*output)(struct sk_buff *skb);
 	struct sk_buff_head	arp_queue;
 	struct timer_list	timer;
-	struct neigh_ops	*ops;
+	const struct neigh_ops	*ops;
 	u8			primary_key[0];
 };