[TCP]: Return useful listenq info in tcp_info and INET_DIAG_INFO.

Return some useful information such as the maximum listen backlog and
the current listen backlog in the tcp_info structure and
INET_DIAG_INFO.
Signed-off-by: Rick Jones <rick.jones2@hp.com>
Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/tcp.c

@@ -2031,8 +2031,13 @@ void tcp_get_info(struct sock *sk, struct tcp_info *info)
 	info->tcpi_snd_mss = tp->mss_cache;
 	info->tcpi_rcv_mss = icsk->icsk_ack.rcv_mss;
 
+	if (sk->sk_state == TCP_LISTEN) {
+		info->tcpi_unacked = sk->sk_ack_backlog;
+		info->tcpi_sacked = sk->sk_max_ack_backlog;
+	} else {
 		info->tcpi_unacked = tp->packets_out;
 		info->tcpi_sacked = tp->sacked_out;
+	}
 	info->tcpi_lost = tp->lost_out;
 	info->tcpi_retrans = tp->retrans_out;
 	info->tcpi_fackets = tp->fackets_out;

net/ipv4/tcp_diag.c

@@ -25,11 +25,13 @@ static void tcp_diag_get_info(struct sock *sk, struct inet_diag_msg *r,
 	const struct tcp_sock *tp = tcp_sk(sk);
 	struct tcp_info *info = _info;
 
-	if (sk->sk_state == TCP_LISTEN)
+	if (sk->sk_state == TCP_LISTEN) {
 		r->idiag_rqueue = sk->sk_ack_backlog;
-	else
+		r->idiag_wqueue = sk->sk_max_ack_backlog;
+	} else {
 		r->idiag_rqueue = tp->rcv_nxt - tp->copied_seq;
 		r->idiag_wqueue = tp->write_seq - tp->snd_una;
+	}
 	if (info != NULL)
 		tcp_get_info(sk, info);
 }