via-rhine: Fix bugs in NAPI support.

1) rhine_tx() should use dev_kfree_skb() not dev_kfree_skb_irq()

2) rhine_slow_event_task's NAPI triggering logic is racey, it
   should just hit the interrupt mask register.  This is the
   same as commit 7dbb4918
   ("r8169: avoid NAPI scheduling delay.") made to fix the same
   problem in the r8169 driver.  From Francois Romieu.
Reported-by: Jamie Gloudon <jamie.gloudon@gmail.com>
Tested-by: Jamie Gloudon <jamie.gloudon@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/via/via-rhine.c

@@ -1801,7 +1801,7 @@ static void rhine_tx(struct net_device *dev)
 					 rp->tx_skbuff[entry]->len,
 					 PCI_DMA_TODEVICE);
 		}
-		dev_kfree_skb_irq(rp->tx_skbuff[entry]);
+		dev_kfree_skb(rp->tx_skbuff[entry]);
 		rp->tx_skbuff[entry] = NULL;
 		entry = (++rp->dirty_tx) % TX_RING_SIZE;
 	}
@@ -2010,11 +2010,7 @@ static void rhine_slow_event_task(struct work_struct *work)
 	if (intr_status & IntrPCIErr)
 		netif_warn(rp, hw, dev, "PCI error\n");
 
-	napi_disable(&rp->napi);
-	rhine_irq_disable(rp);
-	/* Slow and safe. Consider __napi_schedule as a replacement ? */
-	napi_enable(&rp->napi);
-	napi_schedule(&rp->napi);
+	iowrite16(RHINE_EVENT & 0xffff, rp->base + IntrEnable);
 
 out_unlock:
 	mutex_unlock(&rp->task_lock);