make XWayland clients inherit tags and monitors

Revert 3213088 because the linked bug can no longer be reproduced with
wlroots 0.17, and update client_get_parent() so it doesn't segfault with
XWayland surfaces. This also allows reusing the p variable in the next
commit.

dwl.c

@@ -1542,8 +1542,7 @@ mapnotify(struct wl_listener *listener, void *data)
 	 * we always consider floating, clients that have parent and thus
 	 * we set the same tags and monitor than its parent, if not
 	 * try to apply rules for them */
-	/* TODO: https://github.com/djpohly/dwl/pull/334#issuecomment-1330166324 */
-	if (c->type == XDGShell && (p = client_get_parent(c))) {
+	if ((p = client_get_parent(c))) {
 		c->isfloating = 1;
 		setmon(c, p->mon, p->tags);
 	} else {