code: func IsVersionNegotiationPacket(b []byte) bool {
  	if len(b) < 5 {
  		return false
  	}
  	return b[0]&0x80 > 0 && b[1] == 0 && b[2] == 0 && b[3] == 0 && b[4] == 0
  }
docs: // IsVersionNegotiationPacket says if this is a version negotiation packet