wayland: Ensure modal hint gets set on map
wayland: Ensure modal hint gets set on map

We need to be mapped to have a gtk_surface and thus be able to do
requests on it so we need to save the modal hint and apply it when we
get mapped so that code that sets the hint before showing a window
doesn't get ignored.

https://bugzilla.gnome.org/show_bug.cgi?id=753138

jadahl/gtk,jigpu/gtk,grubersjoe/adwaita,alexlarsson/gtk,jadahl/gtk,chergert/gtk,chergert/gtk,grubersjoe/adwaita,grubersjoe/adwaita,chergert/gtk,chergert/gtk,grubersjoe/adwaita,jigpu/gtk,jigpu/gtk,chergert/gtk,jadahl/gtk,jigpu/gtk,davidgumberg/gtk,alexlarsson/gtk,davidgumberg/gtk,grubersjoe/adwaita,alexlarsson/gtk,alexlarsson/gtk,jigpu/gtk,jigpu/gtk,davidgumberg/gtk,chergert/gtk,jadahl/gtk,alexlarsson/gtk,davidgumberg/gtk,chergert/gtk,grubersjoe/adwaita,chergert/gtk,jadahl/gtk,jigpu/gtk,jigpu/gtk,jadahl/gtk,jadahl/gtk,alexlarsson/gtk,grubersjoe/adwaita,davidgumberg/gtk,jadahl/gtk,davidgumberg/gtk,davidgumberg/gtk,alexlarsson/gtk,alexlarsson/gtk,grubersjoe/adwaita,davidgumberg/gtk