net: bcmgenet: correctly pad short packets

Packets shorter than ETH_ZLEN were not padded with zeroes, hence leaking
potentially sensitive information. This bug has been present since the
driver got accepted in commit 1c1008c7
("net: bcmgenet: add main driver file").
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/broadcom/genet/bcmgenet.c

@@ -1149,6 +1149,11 @@ static netdev_tx_t bcmgenet_xmit(struct sk_buff *skb, struct net_device *dev)
 		goto out;
 	}
 
+	if (skb_padto(skb, ETH_ZLEN)) {
+		ret = NETDEV_TX_OK;
+		goto out;
+	}
+
 	/* set the SKB transmit checksum */
 	if (priv->desc_64b_en) {
 		ret = bcmgenet_put_tx_csum(dev, skb);