net: add skb frag size accessors

To ease skb->truesize sanitization, its better to be able to localize
all references to skb frags size.

Define accessors : skb_frag_size() to fetch frag size, and
skb_frag_size_{set|add|sub}() to manipulate it.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/ethernet/broadcom/bnx2.c b/drivers/net/ethernet/broadcom/bnx2.c
index 6ff7636..965c723 100644
--- a/drivers/net/ethernet/broadcom/bnx2.c
+++ b/drivers/net/ethernet/broadcom/bnx2.c
@@ -2871,7 +2871,7 @@
 				dma_unmap_addr(
 					&txr->tx_buf_ring[TX_RING_IDX(sw_cons)],
 					mapping),
-				skb_shinfo(skb)->frags[i].size,
+				skb_frag_size(&skb_shinfo(skb)->frags[i]),
 				PCI_DMA_TODEVICE);
 		}
 
@@ -3049,7 +3049,7 @@
 				} else {
 					skb_frag_t *frag =
 						&skb_shinfo(skb)->frags[i - 1];
-					frag->size -= tail;
+					skb_frag_size_sub(frag, tail);
 					skb->data_len -= tail;
 				}
 				return 0;
@@ -5395,7 +5395,7 @@
 				tx_buf = &txr->tx_buf_ring[TX_RING_IDX(j)];
 				dma_unmap_page(&bp->pdev->dev,
 					dma_unmap_addr(tx_buf, mapping),
-					skb_shinfo(skb)->frags[k].size,
+					skb_frag_size(&skb_shinfo(skb)->frags[k]),
 					PCI_DMA_TODEVICE);
 			}
 			dev_kfree_skb(skb);
@@ -6530,13 +6530,13 @@
 	tx_buf->is_gso = skb_is_gso(skb);
 
 	for (i = 0; i < last_frag; i++) {
-		skb_frag_t *frag = &skb_shinfo(skb)->frags[i];
+		const skb_frag_t *frag = &skb_shinfo(skb)->frags[i];
 
 		prod = NEXT_TX_BD(prod);
 		ring_prod = TX_RING_IDX(prod);
 		txbd = &txr->tx_desc_ring[ring_prod];
 
-		len = frag->size;
+		len = skb_frag_size(frag);
 		mapping = skb_frag_dma_map(&bp->pdev->dev, frag, 0, len,
 					   DMA_TO_DEVICE);
 		if (dma_mapping_error(&bp->pdev->dev, mapping))
@@ -6594,7 +6594,7 @@
 		ring_prod = TX_RING_IDX(prod);
 		tx_buf = &txr->tx_buf_ring[ring_prod];
 		dma_unmap_page(&bp->pdev->dev, dma_unmap_addr(tx_buf, mapping),
-			       skb_shinfo(skb)->frags[i].size,
+			       skb_frag_size(&skb_shinfo(skb)->frags[i]),
 			       PCI_DMA_TODEVICE);
 	}