チャンネルに可能な最大パケットサイズを設定するオプション
It is possible to set a maximum packet size for a connection in the transport layer using the ConnectionConfig class, and globally using the GlobalConfig class. This option allows the maximum packet size for an individual channel to be set. This can only be set to less than the connection's maximum packets size, not more. This can only be done before sending any data on the connection.