MEDIUM: stream-int/conn-stream: Move blocking flags from SI to CS

MEDIUM: stream-int/conn-stream: Move blocking flags from SI to CS

Remaining flags and associated functions are move in the conn-stream
scope. These flags are added on the endpoint and not the conn-stream
itself. This way it will be possible to get them from the mux or the
applet. The functions to get or set these flags are renamed accordingly with
the "cs_" prefix and updated to manipualte a conn-stream instead of a
stream-interface.