tg3: Add skb->xmit_more support

Ring TX doorbell only if xmit_more is not set or the queue is stopped.
Suggested-by: NDaniel Borkmann <dborkman@redhat.com>
Signed-off-by: NPrashant Sreedharan <prashant@broadcom.com>
Signed-off-by: NMichael Chan <mchan@broadcom.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ethernet/broadcom/tg3.c

@@ -8099,9 +8099,6 @@ static netdev_tx_t tg3_start_xmit(struct sk_buff *skb, struct net_device *dev)
 	/* Sync BD data before updating mailbox */
 	wmb();
 
-	/* Packets are ready, update Tx producer idx local and on card. */
-	tw32_tx_mbox(tnapi->prodmbox, entry);
-
 	tnapi->tx_prod = entry;
 	if (unlikely(tg3_tx_avail(tnapi) <= (MAX_SKB_FRAGS + 1))) {
 		netif_tx_stop_queue(txq);
@@ -8116,7 +8113,12 @@ static netdev_tx_t tg3_start_xmit(struct sk_buff *skb, struct net_device *dev)
 			netif_tx_wake_queue(txq);
 	}
 
-	mmiowb();
+	if (!skb->xmit_more || netif_xmit_stopped(txq)) {
+		/* Packets are ready, update Tx producer idx on card. */
+		tw32_tx_mbox(tnapi->prodmbox, entry);
+		mmiowb();
+	}
+
 	return NETDEV_TX_OK;
 
 dma_error: