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/rt2400pci.c b/drivers/net/wireless/rt2x00/rt2400pci.c
index 08a4789..6f89891 100644
--- a/drivers/net/wireless/rt2x00/rt2400pci.c
+++ b/drivers/net/wireless/rt2x00/rt2400pci.c
@@ -1017,8 +1017,8 @@
 	rt2x00_desc_write(entry_priv->desc, 1, word);
 
 	rt2x00_desc_read(txd, 2, &word);
-	rt2x00_set_field32(&word, TXD_W2_BUFFER_LENGTH, skb->len);
-	rt2x00_set_field32(&word, TXD_W2_DATABYTE_COUNT, skb->len);
+	rt2x00_set_field32(&word, TXD_W2_BUFFER_LENGTH, txdesc->length);
+	rt2x00_set_field32(&word, TXD_W2_DATABYTE_COUNT, txdesc->length);
 	rt2x00_desc_write(txd, 2, word);
 
 	rt2x00_desc_read(txd, 3, &word);