ieee802154: create 6lowpan sub-directory

This patch creates an 6lowpan sub-directory inside ieee802154.
Additional we move all ieee802154 6lowpan relevant files into
this sub-directory instead of placing the 6lowpan related files
inside ieee802154.

Signed-off-by: Alexander Aring <alex.aring@gmail.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
diff --git a/net/ieee802154/Kconfig b/net/ieee802154/Kconfig
index 9ea0af4..1370d5b 100644
--- a/net/ieee802154/Kconfig
+++ b/net/ieee802154/Kconfig
@@ -20,10 +20,6 @@
 	  for 802.15.4 dataframes. Also RAW socket interface to build MAC
 	  header from userspace.
 
-config IEEE802154_6LOWPAN
-	tristate "6lowpan support over IEEE 802.15.4"
-	depends on 6LOWPAN
-	---help---
-	  IPv6 compression over IEEE 802.15.4.
+source "net/ieee802154/6lowpan/Kconfig"
 
 endif