code: func (c *cubicState) reduceSlowStartThreshold() {
  	c.s.sndSsthresh = int(math.Max(float64(c.s.sndCwnd)*c.beta, 2.0))
  }
docs: // reduceSlowStartThreshold returns new SsThresh as described in
  // https://tools.ietf.org/html/rfc8312#section-4.7.