6lowpan: clarify Kconfig entries for upcoming GHC support

Acked-by: Jukka Rissanen <[e-mail]>
Signed-off-by: Stefan Schmidt <[e-mail]>
Signed-off-by: Alexander Aring <[e-mail]>
Signed-off-by: Marcel Holtmann <[e-mail]>

net/6lowpan/Kconfig

···
 	  "6LoWPAN" which is supported by IEEE 802.15.4 or Bluetooth stacks.
 
 menuconfig 6LOWPAN_NHC
-	tristate "Next Header Compression Support"
+	tristate "Next Header and Generic Header Compression Support"
 	depends on 6LOWPAN
 	default y
 	---help---
-	  Support for next header compression.
+	  Support for next header and generic header compression defined in
+	  RFC6282 and RFC7400.
 
 if 6LOWPAN_NHC