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/ibm/ehea/ehea_main.c b/drivers/net/ethernet/ibm/ehea/ehea_main.c
index adb462d..0d4d4f6 100644
--- a/drivers/net/ethernet/ibm/ehea/ehea_main.c
+++ b/drivers/net/ethernet/ibm/ehea/ehea_main.c
@@ -1676,7 +1676,7 @@
 
 			/* copy sg1entry data */
 			sg1entry->l_key = lkey;
-			sg1entry->len = frag->size;
+			sg1entry->len = skb_frag_size(frag);
 			sg1entry->vaddr =
 				ehea_map_vaddr(skb_frag_address(frag));
 			swqe->descriptors++;
@@ -1689,7 +1689,7 @@
 			sgentry = &sg_list[i - sg1entry_contains_frag_data];
 
 			sgentry->l_key = lkey;
-			sgentry->len = frag->size;
+			sgentry->len = frag_size(frag);
 			sgentry->vaddr = ehea_map_vaddr(skb_frag_address(frag));
 			swqe->descriptors++;
 		}
diff --git a/drivers/net/ethernet/ibm/emac/core.c b/drivers/net/ethernet/ibm/emac/core.c
index 6b3a033..ed79b2d 100644
--- a/drivers/net/ethernet/ibm/emac/core.c
+++ b/drivers/net/ethernet/ibm/emac/core.c
@@ -1453,7 +1453,7 @@
 	/* skb fragments */
 	for (i = 0; i < nr_frags; ++i) {
 		struct skb_frag_struct *frag = &skb_shinfo(skb)->frags[i];
-		len = frag->size;
+		len = skb_frag_size(frag);
 
 		if (unlikely(dev->tx_cnt + mal_tx_chunks(len) >= NUM_TX_BUFF))
 			goto undo_frame;
diff --git a/drivers/net/ethernet/ibm/ibmveth.c b/drivers/net/ethernet/ibm/ibmveth.c
index 4da972e..b1cd41b 100644
--- a/drivers/net/ethernet/ibm/ibmveth.c
+++ b/drivers/net/ethernet/ibm/ibmveth.c
@@ -1014,15 +1014,15 @@
 
 	/* Map the frags */
 	for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
-		skb_frag_t *frag = &skb_shinfo(skb)->frags[i];
+		const skb_frag_t *frag = &skb_shinfo(skb)->frags[i];
 
 		dma_addr = skb_frag_dma_map(&adapter->vdev->dev, frag, 0,
-					    frag->size, DMA_TO_DEVICE);
+					    skb_frag_size(frag), DMA_TO_DEVICE);
 
 		if (dma_mapping_error(&adapter->vdev->dev, dma_addr))
 			goto map_failed_frags;
 
-		descs[i+1].fields.flags_len = desc_flags | frag->size;
+		descs[i+1].fields.flags_len = desc_flags | skb_frag_size(frag);
 		descs[i+1].fields.address = dma_addr;
 	}