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/arp.h b/include/net/arp.h
index c236270..716f43c 100644
--- a/include/net/arp.h
+++ b/include/net/arp.h
@@ -26,6 +26,6 @@
 				  const unsigned char *target_hw);
 extern void arp_xmit(struct sk_buff *skb);
 
-extern struct neigh_ops arp_broken_ops;
+extern const struct neigh_ops arp_broken_ops;
 
 #endif	/* _ARP_H */