[SK_BUFF]: Introduce skb_copy_from_linear_data{_offset}

To clearly state the intent of copying from linear sk_buffs, _offset being a
overly long variant but interesting for the sake of saving some bytes.

Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
diff --git a/drivers/s390/net/ctcmain.c b/drivers/s390/net/ctcmain.c
index 54e3f80..b0f813e 100644
--- a/drivers/s390/net/ctcmain.c
+++ b/drivers/s390/net/ctcmain.c
@@ -472,7 +472,8 @@
 			privptr->stats.rx_dropped++;
 			return;
 		}
-		memcpy(skb_put(skb, pskb->len), pskb->data, pskb->len);
+		skb_copy_from_linear_data(pskb, skb_put(skb, pskb->len),
+					  pskb->len);
 		skb_reset_mac_header(skb);
 		skb->dev = pskb->dev;
 		skb->protocol = pskb->protocol;
@@ -716,8 +717,9 @@
 		*((__u16 *) skb_put(ch->trans_skb, 2)) = ch->collect_len + 2;
 		i = 0;
 		while ((skb = skb_dequeue(&ch->collect_queue))) {
-			memcpy(skb_put(ch->trans_skb, skb->len), skb->data,
-			       skb->len);
+			skb_copy_from_linear_data(skb, skb_put(ch->trans_skb,
+							       skb->len),
+						  skb->len);
 			privptr->stats.tx_packets++;
 			privptr->stats.tx_bytes += skb->len - LL_HEADER_LENGTH;
 			atomic_dec(&skb->users);
@@ -2268,8 +2270,9 @@
 			skb_reset_tail_pointer(ch->trans_skb);
 			ch->trans_skb->len = 0;
 			ch->ccw[1].count = skb->len;
-			memcpy(skb_put(ch->trans_skb, skb->len), skb->data,
-			       skb->len);
+			skb_copy_from_linear_data(skb, skb_put(ch->trans_skb,
+							       skb->len),
+						  skb->len);
 			atomic_dec(&skb->users);
 			dev_kfree_skb_irq(skb);
 			ccw_idx = 0;