Backported from X.org:

  commit 491cf02e191e70c5ce24c19da880bb79bebfc03c
  Author: Jon TURNEY <jon.turney@dronecode.org.uk>
  Date:   Tue Feb 10 2015 14:37:26 +0000

    [PATCH] os: XDMCP options like -query etc. should imply -listen tcp

    In X server 1.17, the default configuration is now -nolisten tcp.  In this
    configuration, XDMCP options don't work usefully, as the X server is not
    listening on the port for the display that it tells the display manager to
    connect to.
Signed-off-by: Jon TURNEY <jon.turney@dronecode.org.uk>
Reviewed-by: Alan Coopersmith <alan.coopersmith@oracle.com>
Reviewed-by: Colin Harrison <colin.harrison@virgin.net>

Backported-to-NX-by: Mihai Moldovan <ionic@ionic.de