rt2x00: Register frame length in TX entry descriptor instead of L2PAD.

And use it consistently in the chipset drivers.
Preparation for further clean ups.

Signed-off-by: Gertjan van Wingerde <gwingerde@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/drivers/net/wireless/rt2x00/rt73usb.c b/drivers/net/wireless/rt2x00/rt73usb.c
index 7ebe14b..1399c18 100644
--- a/drivers/net/wireless/rt2x00/rt73usb.c
+++ b/drivers/net/wireless/rt2x00/rt73usb.c
@@ -1494,7 +1494,7 @@
 	rt2x00_set_field32(&word, TXD_W0_KEY_TABLE,
 			   test_bit(ENTRY_TXD_ENCRYPT_PAIRWISE, &txdesc->flags));
 	rt2x00_set_field32(&word, TXD_W0_KEY_INDEX, txdesc->key_idx);
-	rt2x00_set_field32(&word, TXD_W0_DATABYTE_COUNT, skb->len);
+	rt2x00_set_field32(&word, TXD_W0_DATABYTE_COUNT, txdesc->length);
 	rt2x00_set_field32(&word, TXD_W0_BURST2,
 			   test_bit(ENTRY_TXD_BURST, &txdesc->flags));
 	rt2x00_set_field32(&word, TXD_W0_CIPHER_ALG, txdesc->cipher);