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>

net/ieee802154/6lowpan/Kconfig

+config IEEE802154_6LOWPAN
+	tristate "6lowpan support over IEEE 802.15.4"
+	depends on 6LOWPAN
+	---help---
+	  IPv6 compression over IEEE 802.15.4.

net/ieee802154/6lowpan/Makefile

+obj-y += ieee802154_6lowpan.o
+
+ieee802154_6lowpan-y := 6lowpan_rtnl.o reassembly.o

net/ieee802154/Kconfig

@@ -20,10 +20,6 @@ config IEEE802154_SOCKET
 	  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

net/ieee802154/Makefile

 obj-$(CONFIG_IEEE802154) += ieee802154.o
 obj-$(CONFIG_IEEE802154_SOCKET) += ieee802154_socket.o
-obj-$(CONFIG_IEEE802154_6LOWPAN) += ieee802154_6lowpan.o
+obj-$(CONFIG_IEEE802154_6LOWPAN) += 6lowpan/
 
-ieee802154_6lowpan-y := 6lowpan_rtnl.o reassembly.o
 ieee802154-y := netlink.o nl-mac.o nl-phy.o nl_policy.o core.o \
                 header_ops.o sysfs.o nl802154.o
 ieee802154_socket-y := socket.o