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/rt2500usb.c b/drivers/net/wireless/rt2x00/rt2500usb.c
index c1eec17..c6e6e7b 100644
--- a/drivers/net/wireless/rt2x00/rt2500usb.c
+++ b/drivers/net/wireless/rt2x00/rt2500usb.c
@@ -1071,7 +1071,7 @@
 	rt2x00_set_field32(&word, TXD_W0_NEW_SEQ,
 			   test_bit(ENTRY_TXD_FIRST_FRAGMENT, &txdesc->flags));
 	rt2x00_set_field32(&word, TXD_W0_IFS, txdesc->ifs);
-	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_CIPHER, !!txdesc->cipher);
 	rt2x00_set_field32(&word, TXD_W0_KEY_ID, txdesc->key_idx);
 	rt2x00_desc_write(txd, 0, word);