code: func (whisper *Whisper) SetMaxMessageSize(size uint32) error {
  	if size > MaxMessageSize {
  		return fmt.Errorf("message size too large [%d>%d]", size, MaxMessageSize)
  	}
  	whisper.settings.Store(maxMsgSizeIdx, size)
  	return nil
  }
docs: // SetMaxMessageSize sets the maximal message size allowed by this node