e1000: add and use e1000_rx_buffer info for Rx

e1000 uses the same metadata struct for Rx and Tx.  But Tx and Rx have
different requirements.

For Rx, we only need to store a buffer and a DMA address.

Follow-up patch will remove skb for Rx, bringing rx_buffer_info down
to 16 bytes on x86_64.

[ buffer_info is 48 bytes ]

Signed-off-by: Florian Westphal <fw@strlen.de>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
diff --git a/drivers/net/ethernet/intel/e1000/e1000_ethtool.c b/drivers/net/ethernet/intel/e1000/e1000_ethtool.c
index 9b50272..5ebc240 100644
--- a/drivers/net/ethernet/intel/e1000/e1000_ethtool.c
+++ b/drivers/net/ethernet/intel/e1000/e1000_ethtool.c
@@ -968,7 +968,7 @@
 			if (rxdr->buffer_info[i].dma)
 				dma_unmap_single(&pdev->dev,
 						 rxdr->buffer_info[i].dma,
-						 rxdr->buffer_info[i].length,
+						 E1000_RXBUFFER_2048,
 						 DMA_FROM_DEVICE);
 			if (rxdr->buffer_info[i].skb)
 				dev_kfree_skb(rxdr->buffer_info[i].skb);
@@ -1065,7 +1065,7 @@
 	if (!rxdr->count)
 		rxdr->count = E1000_DEFAULT_RXD;
 
-	rxdr->buffer_info = kcalloc(rxdr->count, sizeof(struct e1000_buffer),
+	rxdr->buffer_info = kcalloc(rxdr->count, sizeof(struct e1000_rx_buffer),
 				    GFP_KERNEL);
 	if (!rxdr->buffer_info) {
 		ret_val = 5;
@@ -1104,7 +1104,6 @@
 		}
 		skb_reserve(skb, NET_IP_ALIGN);
 		rxdr->buffer_info[i].skb = skb;
-		rxdr->buffer_info[i].length = E1000_RXBUFFER_2048;
 		rxdr->buffer_info[i].dma =
 			dma_map_single(&pdev->dev, skb->data,
 				       E1000_RXBUFFER_2048, DMA_FROM_DEVICE);
@@ -1440,7 +1439,7 @@
 		do { /* receive the sent packets */
 			dma_sync_single_for_cpu(&pdev->dev,
 						rxdr->buffer_info[l].dma,
-						rxdr->buffer_info[l].length,
+						E1000_RXBUFFER_2048,
 						DMA_FROM_DEVICE);
 
 			ret_val = e1000_check_lbtest_frame(