[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>

drivers/bluetooth/bfusb.c

@@ -527,7 +527,7 @@ static int bfusb_send_frame(struct sk_buff *skb)
 		buf[2] = (size == BFUSB_MAX_BLOCK_SIZE) ? 0 : size;
 
 		memcpy(skb_put(nskb, 3), buf, 3);
-		memcpy(skb_put(nskb, size), skb->data + sent, size);
+		skb_copy_from_linear_data_offset(skb, sent, skb_put(nskb, size), size);
 
 		sent  += size;
 		count -= size;