ax25: Refactor to use private neighbour operations.

AX25 already has it's own private arp cache operations to isolate
it's abuse of dev_rebuild_header to transmit packets.  Add a function
ax25_neigh_construct that will allow all of the ax25 devices to
force using these operations, so that the generic arp code does
not need to.

Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: linux-hams@vger.kernel.org
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/hamradio/mkiss.c

@@ -641,6 +641,7 @@ static const struct net_device_ops ax_netdev_ops = {
 	.ndo_stop            = ax_close,
 	.ndo_start_xmit	     = ax_xmit,
 	.ndo_set_mac_address = ax_set_mac_address,
+	.ndo_neigh_construct = ax25_neigh_construct,
 };
 
 static void ax_setup(struct net_device *dev)
@@ -650,6 +651,7 @@ static void ax_setup(struct net_device *dev)
 	dev->hard_header_len = 0;
 	dev->addr_len        = 0;
 	dev->type            = ARPHRD_AX25;
+	dev->neigh_priv_len  = sizeof(struct ax25_neigh_priv);
 	dev->tx_queue_len    = 10;
 	dev->header_ops      = &ax25_header_ops;
 	dev->netdev_ops	     = &ax_netdev_ops;