code: func IsV4MulticastAddress(addr net.IP) bool {
  	if len(addr) != IPv4AddressSize {
  		return false
  	}
  	return (addr[0] & 0xf0) == 0xe0
  }
docs: // IsV4MulticastAddress determines if the provided address is an IPv4 multicast
  // address (range 224.0.0.0 to 239.255.255.255). The four most significant bits
  // will be 1110 = 0xe0.