ieee802154: rework wpan_phy index assignment

This patch reworks the wpan_phy index incrementation. It's now similar
like wireless wiphy index incrementation. We move the wpan_phy index
attribute inside of cfg802154_registered_device and use atomic
operations instead locking mechanism via wpan_phy_mutex.

Signed-off-by: Alexander Aring <alex.aring@gmail.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
diff --git a/net/ieee802154/core.h b/net/ieee802154/core.h
index 1bc1725..fea60b3 100644
--- a/net/ieee802154/core.h
+++ b/net/ieee802154/core.h
@@ -6,6 +6,9 @@
 struct cfg802154_registered_device {
 	const struct cfg802154_ops *ops;
 
+	/* wpan_phy index, internal only */
+	int wpan_phy_idx;
+
 	/* must be last because of the way we do wpan_phy_priv(),
 	 * and it should at least be aligned to NETDEV_ALIGN
 	 */