bnx2: Add prefetches to rx path.

Add prefetches of the skb and the next rx descriptor to speed up rx path.

Use prefetchw() for the skb [suggested by Eric Dumazet].

The rx descriptor is in skb->data which is mapped for streaming mode DMA.
Eric Dumazet pointed out that we should not prefetch the data before
dma_sync.  So we prefetch only if dma_sync is no_op on the system.

Signed-off-by: Michael Chan <mchan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/bnx2.h b/drivers/net/bnx2.h
index ab34a5d..dd35bd0 100644
--- a/drivers/net/bnx2.h
+++ b/drivers/net/bnx2.h
@@ -6551,6 +6551,7 @@
 
 struct sw_bd {
 	struct sk_buff		*skb;
+	struct l2_fhdr		*desc;
 	DEFINE_DMA_UNMAP_ADDR(mapping);
 };