xwm: make X windows of type 'utility' inactive

Skype's popup notifications use this type.
diff --git a/xwayland/window-manager.c b/xwayland/window-manager.c
index cab7e20..039f0cd 100644
--- a/xwayland/window-manager.c
+++ b/xwayland/window-manager.c
@@ -2423,7 +2423,8 @@
 	       window->type == wm->atom.net_wm_window_type_dropdown ||
 	       window->type == wm->atom.net_wm_window_type_dnd ||
 	       window->type == wm->atom.net_wm_window_type_combo ||
-	       window->type == wm->atom.net_wm_window_type_popup;
+	       window->type == wm->atom.net_wm_window_type_popup ||
+	       window->type == wm->atom.net_wm_window_type_utility;
 }
 
 static void