ieee802154: constify struct net_device in some operations

Some of ieee802154 operations really shouldn't change passed net_device.
Constify passed argument.

Signed-off-by: Dmitry Eremin-Solenikov <dbaryshkov@gmail.com>
diff --git a/include/net/ieee802154_netdev.h b/include/net/ieee802154_netdev.h
index 5dc6a61..d23fb5a 100644
--- a/include/net/ieee802154_netdev.h
+++ b/include/net/ieee802154_netdev.h
@@ -98,14 +98,14 @@
 	 * FIXME: these should become the part of PIB/MIB interface.
 	 * However we still don't have IB interface of any kind
 	 */
-	u16 (*get_pan_id)(struct net_device *dev);
-	u16 (*get_short_addr)(struct net_device *dev);
-	u8 (*get_dsn)(struct net_device *dev);
-	u8 (*get_bsn)(struct net_device *dev);
+	u16 (*get_pan_id)(const struct net_device *dev);
+	u16 (*get_short_addr)(const struct net_device *dev);
+	u8 (*get_dsn)(const struct net_device *dev);
+	u8 (*get_bsn)(const struct net_device *dev);
 };
 
 static inline struct ieee802154_mlme_ops *ieee802154_mlme_ops(
-		struct net_device *dev)
+		const struct net_device *dev)
 {
 	return dev->ml_priv;
 }