[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/net/pppoe.c b/drivers/net/pppoe.c
index e947906..e9fb616 100644
--- a/drivers/net/pppoe.c
+++ b/drivers/net/pppoe.c
@@ -869,7 +869,8 @@
 			goto abort;
 
 		skb_reserve(skb2, dev->hard_header_len + sizeof(struct pppoe_hdr));
-		memcpy(skb_put(skb2, skb->len), skb->data, skb->len);
+		skb_copy_from_linear_data(skb, skb_put(skb2, skb->len),
+					  skb->len);
 	} else {
 		/* Make a clone so as to not disturb the original skb,
 		 * give dev_queue_xmit something it can free.