[SK_BUFF]: Introduce skb_copy_to_linear_data{_offset}

To clearly state the intent of copying to 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@ghostprotocols.net>
diff --git a/net/irda/irttp.c b/net/irda/irttp.c
index b55bc8f..3279897 100644
--- a/net/irda/irttp.c
+++ b/net/irda/irttp.c
@@ -256,7 +256,7 @@
 	 *  Copy all fragments to a new buffer
 	 */
 	while ((frag = skb_dequeue(&self->rx_fragments)) != NULL) {
-		memcpy(skb->data+n, frag->data, frag->len);
+		skb_copy_to_linear_data_offset(skb, n, frag->data, frag->len);
 		n += frag->len;
 
 		dev_kfree_skb(frag);