[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/irda/irda-usb.c b/drivers/net/irda/irda-usb.c
index 6ef375a..0ac240c 100644
--- a/drivers/net/irda/irda-usb.c
+++ b/drivers/net/irda/irda-usb.c
@@ -441,7 +441,7 @@
 		goto drop;
 	}
 
-	memcpy(self->tx_buff + self->header_length, skb->data, skb->len);
+	skb_copy_from_linear_data(skb, self->tx_buff + self->header_length, skb->len);
 
 	/* Change setting for next frame */
 	if (self->capability & IUC_STIR421X) {
@@ -902,7 +902,7 @@
 
 	if(docopy) {
 		/* Copy packet, so we can recycle the original */
-		memcpy(newskb->data, skb->data, urb->actual_length);
+		skb_copy_from_linear_data(skb, newskb->data, urb->actual_length);
 		/* Deliver this new skb */
 		dataskb = newskb;
 		/* And hook the old skb to the URB