6lowpan: add lowpan dev register helpers

This patch introduces register and unregister functionality for lowpan
interfaces. While register a lowpan interface there are several things
which need to be initialize by the 6lowpan subsystem. Upcoming
functionality need to register/unregister per interface components e.g.
debugfs entry.

Reviewed-by: Stefan Schmidt <stefan@osg.samsung.com>
Signed-off-by: Alexander Aring <alex.aring@gmail.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
diff --git a/include/net/6lowpan.h b/include/net/6lowpan.h
index cf3bc56..730211f 100644
--- a/include/net/6lowpan.h
+++ b/include/net/6lowpan.h
@@ -185,7 +185,12 @@
 	*hc_ptr += len;
 }
 
-void lowpan_netdev_setup(struct net_device *dev, enum lowpan_lltypes lltype);
+int lowpan_register_netdevice(struct net_device *dev,
+			      enum lowpan_lltypes lltype);
+int lowpan_register_netdev(struct net_device *dev,
+			   enum lowpan_lltypes lltype);
+void lowpan_unregister_netdevice(struct net_device *dev);
+void lowpan_unregister_netdev(struct net_device *dev);
 
 /**
  * lowpan_header_decompress - replace 6LoWPAN header with IPv6 header