r8169: use hardware auto-padding.

It shortens the code and fixes the current pci_unmap leak with
padded skb reported by Dave Jones.

Signed-off-by: Francois Romieu <romieu@fr.zoreil.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/r8169.c

@@ -3363,13 +3363,6 @@ static int rtl8169_start_xmit(struct sk_buff *skb, struct net_device *dev)
 		opts1 |= FirstFrag;
 	} else {
 		len = skb->len;
-
-		if (unlikely(len < ETH_ZLEN)) {
-			if (skb_padto(skb, ETH_ZLEN))
-				goto err_update_stats;
-			len = ETH_ZLEN;
-		}
-
 		opts1 |= FirstFrag | LastFrag;
 		tp->tx_skb[entry].skb = skb;
 	}
@@ -3407,7 +3400,6 @@ out:
 err_stop:
 	netif_stop_queue(dev);
 	ret = NETDEV_TX_BUSY;
-err_update_stats:
 	dev->stats.tx_dropped++;
 	goto out;
 }