tcp: update the netstamp_needed counter when cloning sockets

This fixes a netstamp_needed accounting issue when the listen socket
has SO_TIMESTAMP set:

    s = socket(AF_INET, SOCK_STREAM, 0);
    setsockopt(s, SOL_SOCKET, SO_TIMESTAMP, 1); -> netstamp_needed = 1
    bind(s, ...);
    listen(s, ...);
    s2 = accept(s, ...); -> netstamp_needed = 1
    close(s2); -> netstamp_needed = 0
    close(s); -> netstamp_needed = -1
Signed-off-by: NOctavian Purdila <opurdila@ixiacom.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/core/sock.c

@@ -1205,6 +1205,10 @@ struct sock *sk_clone(const struct sock *sk, const gfp_t priority)
 
 		if (newsk->sk_prot->sockets_allocated)
 			percpu_counter_inc(newsk->sk_prot->sockets_allocated);
+
+		if (sock_flag(newsk, SOCK_TIMESTAMP) ||
+		    sock_flag(newsk, SOCK_TIMESTAMPING_RX_SOFTWARE))
+			net_enable_timestamp();
 	}
 out:
 	return newsk;