ipv6: tcp: send consistent flowlabel in TIME_WAIT state

After commit 1d13a96c ("ipv6: tcp: fix flowlabel value in ACK
messages"), we stored in tw_flowlabel the flowlabel, in the
case ACK packets needed to be sent on behalf of a TIME_WAIT socket.

We can use the same field so that RST packets sent from
TIME_WAIT state also use a consistent flowlabel.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Florent Fourcot <florent.fourcot@wifirst.fr>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/tcp_ipv6.c

@@ -982,6 +982,8 @@ static void tcp_v6_send_reset(const struct sock *sk, struct sk_buff *skb)
 		oif = sk->sk_bound_dev_if;
 		if (sk_fullsock(sk))
 			trace_tcp_send_reset(sk, skb);
+		if (sk->sk_state == TCP_TIME_WAIT)
+			label = cpu_to_be32(inet_twsk(sk)->tw_flowlabel);
 	} else {
 		if (net->ipv6.sysctl.flowlabel_reflect & 2)
 			label = ip6_flowlabel(ipv6h);