xwm: Set WM_STATE window property

xprop and gtk+ dnd is now working.
diff --git a/src/xwayland/xwayland.h b/src/xwayland/xwayland.h
index 26be7de..1b1cdff 100644
--- a/src/xwayland/xwayland.h
+++ b/src/xwayland/xwayland.h
@@ -79,6 +79,7 @@
 		xcb_atom_t		 wm_protocols;
 		xcb_atom_t		 wm_take_focus;
 		xcb_atom_t		 wm_delete_window;
+		xcb_atom_t		 wm_state;
 		xcb_atom_t		 net_wm_name;
 		xcb_atom_t		 net_wm_icon;
 		xcb_atom_t		 net_wm_state;