6lowpan: add udp compression via nhc layer

This patch move UDP header compression and uncompression into the
generic 6LoWPAN nhc header compression layer. Moreover this patch
activates the nhc layer compression in iphc compression and
uncompression functions.

Signed-off-by: Alexander Aring <alex.aring@gmail.com>
Cc: Martin Townsend <mtownsend1973@gmail.com>
Reviewed-by: Stefan Schmidt <s.schmidt@samsung.com>
Acked-by: Jukka Rissanen <jukka.rissanen@linux.intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
diff --git a/net/6lowpan/Kconfig b/net/6lowpan/Kconfig
index e4a02ef..e45c963 100644
--- a/net/6lowpan/Kconfig
+++ b/net/6lowpan/Kconfig
@@ -1,6 +1,23 @@
-config 6LOWPAN
+menuconfig 6LOWPAN
 	tristate "6LoWPAN Support"
 	depends on IPV6
 	---help---
 	  This enables IPv6 over Low power Wireless Personal Area Network -
 	  "6LoWPAN" which is supported by IEEE 802.15.4 or Bluetooth stacks.
+
+menuconfig 6LOWPAN_NHC
+	tristate "Next Header Compression Support"
+	depends on 6LOWPAN
+	default y
+	---help---
+	  Support for next header compression.
+
+if 6LOWPAN_NHC
+
+config 6LOWPAN_NHC_UDP
+	tristate "UDP Header Support"
+	default y
+	---help---
+	  6LoWPAN IPv6 UDP Header compression according to RFC6282.
+
+endif