skb_append(skb_prev, skb);
skb_append(skb_prev, skb, &sk->sk_write_queue);
void x25_requeue_frames(struct sock *sk){	struct sk_buff *skb, *skb_prev = NULL;	/*	 * Requeue all the un-ack-ed frames on the output queue to be picked	 * up by x25_kick. This arrangement handles the possibility of an empty	 * output queue.	 */	while ((skb = skb_dequeue(&x25_sk(sk)->ack_queue)) != NULL) {		if (!skb_prev)			skb_queue_head(&sk->sk_write_queue, skb);		else			skb_append(skb_prev, skb);		skb_prev = skb;	}}