RTAX_WINDOW
#define fib_window fib_metrics->metrics[RTAX_WINDOW-1]
len = put_rtax(mx, len, RTAX_WINDOW, rt->rt_window);
dst_metric(&rt->dst, RTAX_WINDOW);
req->rsk_window_clamp = window_clamp ? : dst_metric(dst, RTAX_WINDOW);
WRITE_ONCE(tp->window_clamp, dst_metric(dst, RTAX_WINDOW));
req->rsk_window_clamp = READ_ONCE(tp->window_clamp) ? :dst_metric(dst, RTAX_WINDOW);