Revert "Tie TcpTransport closedness to its poll_set's nullness."
Revert "Tie TcpTransport closedness to its poll_set's nullness."

This reverts commit a2b77039599b405adc53b2c8d3a88ae41ee92bbd.

nickkazepis/ROS.NET,nickkazepis/ROS.NET,beanstalk42/ROS.NET,uml-robotics/ROS.NET,nickkazepis/ROS.NET