tcp: correct the skip logic in tcp_sacktag_skip()

tcp_sacktag_skip() directly return the input skb only
if TCP_SKB_CB(skb)->seq>skip_to_seq,
this is not right, and  the logic should be
TCP_SKB_CB(skb)->seq>=skip_to_seq, for example
if start_seq is equal to tcp_highest_sack_seq() ,
the start_seq is equal to seq of skb which is from
tcp_highest_sack().
and on the other side ,when
tcp_highest_sack_seq() < start_seq in
tcp_sacktag_write_queue(),
the skb is from tcp_highest_sack() will be ignored
in tcp_sacktag_skip(), so clean the logic also.

Fixes: 75c119a ("tcp: implement rb-tree based retransmit queue")
Signed-off-by: Xin Guo <guoxin0309@gmail.com>
Signed-off-by: NipaLocal <nipa@local>

Author: Xin Guo

net/ipv4/tcp_input.c

@@ -1809,7 +1809,7 @@ static struct sk_buff *tcp_sacktag_bsearch(struct sock *sk, u32 seq)
 static struct sk_buff *tcp_sacktag_skip(struct sk_buff *skb, struct sock *sk,
 					u32 skip_to_seq)
 {
-	if (skb && after(TCP_SKB_CB(skb)->seq, skip_to_seq))
+	if (skb && !before(TCP_SKB_CB(skb)->seq, skip_to_seq))
 		return skb;
 
 	return tcp_sacktag_bsearch(sk, skip_to_seq);
@@ -1997,7 +1997,7 @@ tcp_sacktag_write_queue(struct sock *sk, const struct sk_buff *ack_skb,
 			continue;
 		}
 
-		if (!before(start_seq, tcp_highest_sack_seq(tp))) {
+		if (tcp_highest_sack_seq(tp) == start_seq) {
 			skb = tcp_highest_sack(sk);
 			if (!skb)
 				break;