rt2x00: Move iv_len into tx descriptor data

By placing the iv_len into the tx descriptor data and
by passing this data to the crypto IV handlers we can
save multiple calls to ieee80211_get_hdrlen_from_skb()
and some if-statements when copying/removing the IV data
from the outgoing frame.

Signed-off-by: Ivo van Doorn <IvDoorn@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/rt2x00/rt2x00queue.h

@@ -280,6 +280,7 @@ enum txentry_desc_flags {
  * @cipher: Cipher type used for encryption.
  * @key_idx: Key index used for encryption.
  * @iv_offset: Position where IV should be inserted by hardware.
+ * @iv_len: Length of IV data.
  */
 struct txentry_desc {
 	unsigned long flags;
@@ -302,6 +303,7 @@ struct txentry_desc {
 	enum cipher cipher;
 	u16 key_idx;
 	u16 iv_offset;
+	u16 iv_len;
 };
 
 /**