[NET]: Move destructor from neigh->ops to neigh_params

struct neigh_ops currently has a destructor field, which no in-kernel
drivers outside of infiniband use.  The infiniband/ulp/ipoib in-tree
driver stashes some info in the neighbour structure (the results of
the second-stage lookup from ARP results to real link-level path), and
it uses neigh->ops->destructor to get a callback so it can clean up
this extra info when a neighbour is freed.  We've run into problems
with this: since the destructor is in an ops field that is shared
between neighbours that may belong to different net devices, there's
no way to set/clear it safely.

The following patch moves this field to neigh_parms where it can be
safely set, together with its twin neigh_setup.  Two additional
patches in the patch series update ipoib to use this new interface.

Signed-off-by: Michael S. Tsirkin <mst@mellanox.co.il>
Signed-off-by: Roland Dreier <rolandd@cisco.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/neighbour.h b/include/net/neighbour.h
index 6fa9ae1..b0666d6 100644
--- a/include/net/neighbour.h
+++ b/include/net/neighbour.h
@@ -68,6 +68,7 @@
 	struct net_device *dev;
 	struct neigh_parms *next;
 	int	(*neigh_setup)(struct neighbour *);
+	void	(*neigh_destructor)(struct neighbour *);
 	struct neigh_table *tbl;
 
 	void	*sysctl_table;
@@ -145,7 +146,6 @@
 struct neigh_ops
 {
 	int			family;
-	void			(*destructor)(struct neighbour *);
 	void			(*solicit)(struct neighbour *, struct sk_buff*);
 	void			(*error_report)(struct neighbour *, struct sk_buff*);
 	int			(*output)(struct sk_buff*);