static int pppol2tp_recv_payload_hook(struct sk_buff *skb)
{
	/* Skip PPP header, if present.	 In testing, Microsoft L2TP clients
	 * don't send the PPP header (PPP header compression enabled), but
	 * other clients can include the header. So we cope with both cases
	 * here. The PPP header is always FF03 when using L2TP.
	 *
	 * Note that skb->data[] isn't dereferenced from a u16 ptr here since
	 * the field may be unaligned.
	 */
	if (!pskb_may_pull(skb, 2))
		return 1;

	if ((skb->data[0] == 0xff) && (skb->data[1] == 0x03))
		skb_pull(skb, 2);

	return 0;
}
static int pppol2tp_recv_payload_hook(struct sk_buff *skb)
{
	 
	if (!pskb_may_pull(skb, 2))
		return 1;

	if ((skb->data[0] == 0xff) && (skb->data[1] == 0x03))
		skb_pull(skb, 2);

	return 0;
}