atl1c: Fix misuse of netdev_alloc_skb in refilling rx ring

atl1c uses netdev_alloc_skb to refill its rx dma ring, but that call makes no
guarantees about the suitability of the memory for use in DMA.  As a result
we've gotten reports of atl1c drivers occasionally hanging and needing to be
reset:
https://bugzilla.kernel.org/show_bug.cgi?id=54021

Fix this by modifying the call to use the internal version __netdev_alloc_skb,
where you can set the gfp_mask explicitly to include GFP_DMA.

Tested by two reporters in the above bug, who have the hardware to validate it.
Both report immediate cessation of the problem with this patch
Signed-off-by: Neil Horman <nhorman@tuxdriver.com>
CC: Jay Cliburn <jcliburn@gmail.com>
CC: "David S. Miller" <davem@davemloft.net>
CC: stable@vger.kernel.org
Tested-by: Luis Henriques <luis.henriques@canonical.com>
Tested-by: Vincent Alquier <vincent.alquier@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/atheros/atl1c/atl1c_main.c

@@ -1660,7 +1660,7 @@ static int atl1c_alloc_rx_buffer(struct atl1c_adapter *adapter)
 	while (next_info->flags & ATL1C_BUFFER_FREE) {
 		rfd_desc = ATL1C_RFD_DESC(rfd_ring, rfd_next_to_use);
 
-		skb = netdev_alloc_skb(adapter->netdev, adapter->rx_buffer_len);
+		skb = __netdev_alloc_skb(adapter->netdev, adapter->rx_buffer_len, GFP_ATOMIC|GFP_DMA);
 		if (unlikely(!skb)) {
 			if (netif_msg_rx_err(adapter))
 				dev_warn(&pdev->dev, "alloc rx buffer failed\n");