skb_append(skb_prev, skb);
skb_append(skb_prev, skb, &sk->sk_write_queue);
void nr_requeue_frames(struct sock *sk){	struct sk_buff *skb, *skb_prev = NULL;	while ((skb = skb_dequeue(&nr_sk(sk)->ack_queue)) != NULL) {		if (skb_prev == NULL)			skb_queue_head(&sk->sk_write_queue, skb);		else			skb_append(skb_prev, skb);		skb_prev = skb;	}}