Revert "net: Remove unused neighbour layer ops."

This reverts commit 5c3ddec73d01a1fae9409c197078cb02c42238c3.

S390 qeth driver actually still uses the setup ops.

Reported-by: Frank Blaschka <blaschka@linux.vnet.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 6b9d4ed..6037308 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -974,6 +974,7 @@
 	int			(*ndo_set_features)(struct net_device *dev,
 						    netdev_features_t features);
 	int			(*ndo_neigh_construct)(struct neighbour *n);
+	void			(*ndo_neigh_destroy)(struct neighbour *n);
 };
 
 /*