Allow registering the same coroutine only once as a telnet callback.
Before, it could be registered multiple times. This lead to the situation that the internal telnet callbacks could be registered multiple times in case async_setup method was called multiple times.
Allow registering the same coroutine only once as a telnet callback. Before, it could be registered multiple times. This lead to the situation that the internal telnet callbacks could be registered multiple times in case
async_setupmethod was called multiple times.