[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>

drivers/net/wan/z85230.c

@@ -1656,7 +1656,7 @@ static void z8530_rx_done(struct z8530_channel *c)
 		else
 		{
 			skb_put(skb, ct);
-			memcpy(skb->data, rxb, ct);
+			skb_copy_to_linear_data(skb, rxb, ct);
 			c->stats.rx_packets++;
 			c->stats.rx_bytes+=ct;
 		}