[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/drivers/usb/net/asix.c b/drivers/usb/net/asix.c
index f56e2da..d5ef97b 100644
--- a/drivers/usb/net/asix.c
+++ b/drivers/usb/net/asix.c
@@ -352,7 +352,7 @@
 	skb_push(skb, 4);
 	packet_len = (((skb->len - 4) ^ 0x0000ffff) << 16) + (skb->len - 4);
 	cpu_to_le32s(&packet_len);
-	memcpy(skb->data, &packet_len, sizeof(packet_len));
+	skb_copy_to_linear_data(skb, &packet_len, sizeof(packet_len));
 
 	if ((skb->len % 512) == 0) {
 		cpu_to_le32s(&padbytes);