pxa168_eth: fix race in transmit path.

Because the socket buffer is freed in the completion interrupt, it is not
safe to access it after submitting it to the hardware.

Cc: stable@kernel.org
Cc: Sachin Sanap <ssanap@marvell.com>
Cc: Zhangfei Gao <zgao6@marvell.com>
Cc: Philip Rakity <prakity@marvell.com>
Signed-off-by: NRichard Cochran <richard.cochran@omicron.at>
Acked-by: NEric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/pxa168_eth.c

@@ -1273,7 +1273,7 @@ static int pxa168_eth_start_xmit(struct sk_buff *skb, struct net_device *dev)
 	wmb();
 	wrl(pep, SDMA_CMD, SDMA_CMD_TXDH | SDMA_CMD_ERD);
 
-	stats->tx_bytes += skb->len;
+	stats->tx_bytes += length;
 	stats->tx_packets++;
 	dev->trans_start = jiffies;
 	if (pep->tx_ring_size - pep->tx_desc_count <= 1) {