ath9k_common: add new module to share 802.11n driver helpers

ath9k and ath9k_htc share a lot of common hardware characteristics.
They only differ in that ath9k_htc works with a target CPU and ath9k
works directly with the hardware. ath9k_htc will do *some* things in
the firmware, but a lot of others on the host.

The common 802.11n hardware code is already shared through the ath9k_hw
module. Common helpers amongst all Atheros drivers can use the ath module,
this includes ath5k and ar9170 as users. But there is some common driver
specific helpers which are not exactly hardware code which ath9k and
ath9k_htc can share. We'll be using ath9k_common for this to avoid
bloating the ath module and the common 802.11n hardware module ath9k_hw.

We start by sharing skb pre and post processing in preparation for a hand
off to mac80211.

Signed-off-by: Luis R. Rodriguez <lrodriguez@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/drivers/net/wireless/ath/ath9k/Kconfig b/drivers/net/wireless/ath/ath9k/Kconfig
index b735fb3..006364f 100644
--- a/drivers/net/wireless/ath/ath9k/Kconfig
+++ b/drivers/net/wireless/ath/ath9k/Kconfig
@@ -1,5 +1,7 @@
 config ATH9K_HW
 	tristate
+config ATH9K_COMMON
+	tristate
 
 config ATH9K
 	tristate "Atheros 802.11n wireless cards support"
@@ -8,6 +10,7 @@
 	select MAC80211_LEDS
 	select LEDS_CLASS
 	select NEW_LEDS
+	select ATH9K_COMMON
 	---help---
 	  This module adds support for wireless adapters based on
 	  Atheros IEEE 802.11n AR5008, AR9001 and AR9002 family