tcp: Report mss_clamp with TCP_MAXSEG option in repair mode

The mss_clamp is the only connection-time negotiated option which
cannot be obtained from the user space. Make the TCP_MAXSEG sockopt
report one in the repair mode.
Signed-off-by: NPavel Emelyanov <xemul@openvz.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv4/tcp.c

@@ -2659,6 +2659,8 @@ static int do_tcp_getsockopt(struct sock *sk, int level,
 		val = tp->mss_cache;
 		if (!val && ((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN)))
 			val = tp->rx_opt.user_mss;
+		if (tp->repair)
+			val = tp->rx_opt.mss_clamp;
 		break;
 	case TCP_NODELAY:
 		val = !!(tp->nonagle&TCP_NAGLE_OFF);