MINOR: stream: Only save previous connection state for the server side

MINOR: stream: Only save previous connection state for the server side

The previous connection state on the client side was only used for debugging
purpose to report client close. But this may be handled when the client
stream-interface is switched from SI_ST_DIS to SI_ST_CLO.

So, there only remains the previous connection state on the server side that
is used by the stream, in process_stream(), to be able to set the correct
termination flags. Thus, instead of keeping this info in the
stream-interface for only one side, the info is now stored in the stream
itself.