wl1271: Update TX path block calucation algo

Update the TX path block calculation algorithm based on TI reference.
Signed-off-by: Juuso Oikarinen <juuso.oikarinen@nokia.com>
Reviewed-by: Luciano Coelho <luciano.coelho@nokia.com>
Signed-off-by: Luciano Coelho <luciano.coelho@nokia.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/wl12xx/wl1271_tx.c

@@ -57,8 +57,8 @@ static int wl1271_tx_allocate(struct wl1271 *wl, struct sk_buff *skb, u32 extra)
 	/* approximate the number of blocks required for this packet
 	   in the firmware */
 	/* FIXME: try to figure out what is done here and make it cleaner */
-	total_blocks = (total_len) >> TX_HW_BLOCK_SHIFT_DIV;
-	excluded = (total_blocks << 2) + (skb->len & 0xff) + 34;
+	total_blocks = (total_len + 20) >> TX_HW_BLOCK_SHIFT_DIV;
+	excluded = (total_blocks << 2) + ((total_len + 20) & 0xff) + 34;
 	total_blocks += (excluded > 252) ? 2 : 1;
 	total_blocks += TX_HW_BLOCK_SPARE;