Correctly disable local sessions for xlocal seats using XDMCP.

Approved by PS Jenkins bot, Robert Ancell.

diff --cc src/seat-xlocal.c
index b6a85922d606ec99e99344af0feae5e93bb34a7e,e25752d7c8865657bd7c8c0c93d81711181e19d2..9082be96b253625d085c8ac32f661e82e4ece560
--- 1/src/seat-xlocal.c
--- 2/src/seat-xlocal.c
+++ b/src/seat-xlocal.c
@@@ -246,8 -188,8 +252,9 @@@ seat_xlocal_class_init (SeatXLocalClas
  {
      SeatClass *seat_class = SEAT_CLASS (klass);
  
+     seat_class->get_start_local_sessions = seat_xlocal_get_start_local_sessions;
      seat_class->setup = seat_xlocal_setup;
 +    seat_class->start = seat_xlocal_start;
      seat_class->create_display_server = seat_xlocal_create_display_server;
      seat_class->create_greeter_session = seat_xlocal_create_greeter_session;
      seat_class->create_session = seat_xlocal_create_session;