code: func (sc *Client) SetMaxMessageSize(ctx context.Context, size uint32) error {
  	var ignored bool
  	return sc.c.CallContext(ctx, &ignored, "shh_setMaxMessageSize", size)
  }
docs: // SetMaxMessageSize sets the maximal message size allowed by this node. Incoming
  // and outgoing messages with a larger size will be rejected. Whisper message size
  // can never exceed the limit imposed by the underlying P2P protocol (10 Mb).