sunvnet: failed trigger should not cause BUG_ON()

An error return from __vnet_tx_trigger() sets the TX descriptor to
VIO_DESC_FREE while leaving port->tx_bufs[txi].skb set. This leads
to a BUG_ON() the next time this descriptor is used.

This patch frees the pending skb when getting a trigger error to
match the VIO_DESC_FREE state.
Signed-off-by: David L Stevens <david.stevens@oracle.com>
Acked-by: Sowmini Varadhan <sowmini.varadhan@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/sun/sunvnet.c

@@ -1411,6 +1411,8 @@ static int vnet_start_xmit(struct sk_buff *skb, struct net_device *dev)
 	if (unlikely(err < 0)) {
 		netdev_info(dev, "TX trigger error %d\n", err);
 		d->hdr.state = VIO_DESC_FREE;
+		skb = port->tx_bufs[txi].skb;
+		port->tx_bufs[txi].skb = NULL;
 		dev->stats.tx_carrier_errors++;
 		goto out_dropped;
 	}