code: func GetUnicast(o dhcp6.Options) (IP, error) {
  	v, err := o.GetOne(dhcp6.OptionUnicast)
  	if err != nil {
  		return nil, err
  	}
  
  	var ip IP
  	err = ip.UnmarshalBinary(v)
  	return ip, err
  }
docs: // GetUnicast returns the IP from a Unicast Option value, described in RFC
  // 3315, Section 22.12.
  //
  // The IP return value indicates a server's IPv6 address, which a client may
  // use to contact the server via unicast.