Use async_connect range overload function

[kenba]

The async_connect iterator function is deprecated, see: async_connect
The async_connect range function is preferred, see: async_connect
The comms server shold use the async_connect range function instead of the iterator function.
This should enable the next_socket_ member variable to be removed, since the range function callback contains the newly accepted socket.

[kenba]

incorporated in tag 1.10.2.