mac80211: Let drivers have access to TKIP key offets for TX and RX MIC

Some drivers may want to to use the TKIP key offsets for TX and RX
MIC so lets move this out. Lets also clear up a bit how this is used
internally in mac80211.

Signed-off-by: Luis R. Rodriguez <lrodriguez@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/include/net/mac80211.h b/include/net/mac80211.h
index 7ab4ff6..19f1e41 100644
--- a/include/net/mac80211.h
+++ b/include/net/mac80211.h
@@ -595,7 +595,12 @@
  * @flags: key flags, see &enum ieee80211_key_flags.
  * @keyidx: the key index (0-3)
  * @keylen: key material length
- * @key: key material
+ * @key: key material. For ALG_TKIP the key is encoded as a 256-bit (32 byte)
+ * 	data block:
+ * 	- Temporal Encryption Key (128 bits)
+ * 	- Temporal Authenticator Tx MIC Key (64 bits)
+ * 	- Temporal Authenticator Rx MIC Key (64 bits)
+ *
  */
 struct ieee80211_key_conf {
 	enum ieee80211_key_alg alg;