6lowpan: add private neighbour data

This patch will introduce a 6lowpan neighbour private data. Like the
interface private data we handle private data for generic 6lowpan and
for link-layer specific 6lowpan.

The current first use case if to save the short address for a 802.15.4
6lowpan neighbour.

Cc: David S. Miller <davem@davemloft.net>
Reviewed-by: Stefan Schmidt <stefan@osg.samsung.com>
Acked-by: YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
Signed-off-by: Alexander Aring <aar@pengutronix.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ieee802154/6lowpan/core.c

@@ -81,11 +81,21 @@ static int lowpan_stop(struct net_device *dev)
 	return 0;
 }
 
+static int lowpan_neigh_construct(struct neighbour *n)
+{
+	struct lowpan_802154_neigh *neigh = lowpan_802154_neigh(neighbour_priv(n));
+
+	/* default no short_addr is available for a neighbour */
+	neigh->short_addr = cpu_to_le16(IEEE802154_ADDR_SHORT_UNSPEC);
+	return 0;
+}
+
 static const struct net_device_ops lowpan_netdev_ops = {
 	.ndo_init		= lowpan_dev_init,
 	.ndo_start_xmit		= lowpan_xmit,
 	.ndo_open		= lowpan_open,
 	.ndo_stop		= lowpan_stop,
+	.ndo_neigh_construct    = lowpan_neigh_construct,
 };
 
 static void lowpan_setup(struct net_device *ldev)
@@ -150,6 +160,8 @@ static int lowpan_newlink(struct net *src_net, struct net_device *ldev,
 				wdev->needed_headroom;
 	ldev->needed_tailroom = wdev->needed_tailroom;
 
+	ldev->neigh_priv_len = sizeof(struct lowpan_802154_neigh);
+
 	ret = lowpan_register_netdevice(ldev, LOWPAN_LLTYPE_IEEE802154);
 	if (ret < 0) {
 		dev_put(wdev);