ixgbe: use rx_buffer_info->dma instead of nr_frags to determine skb unmap

This patch changes the driver so that it uses rx_buffer_info->dma to
determine if it needs to unmap the page instead of sh_info->nr_frags.  This
helps to prevent a cache line miss when receiving small packets as the
rx_buffer_info data should already be in the cache.
Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ixgbe/ixgbe_main.c

@@ -708,7 +708,7 @@ static bool ixgbe_clean_rx_irq(struct ixgbe_q_vector *q_vector,
 		prefetch(skb->data - NET_IP_ALIGN);
 		rx_buffer_info->skb = NULL;
 
-		if (len && !skb_shinfo(skb)->nr_frags) {
+		if (rx_buffer_info->dma) {
 			pci_unmap_single(pdev, rx_buffer_info->dma,
 			                 rx_ring->rx_buf_len,
 			                 PCI_DMA_FROMDEVICE);