OPTIM: stream_interface: disable reading when CF_READ_DONTWAIT is set

OPTIM: stream_interface: disable reading when CF_READ_DONTWAIT is set

CF_READ_DONTWAIT was designed to avoid getting an EAGAIN upon recv() when
very few data are expected. It prevents the reader from looping over
recv(). Unfortunately with speculative I/O, it is very common that the
same event has the time to be called twice before the task handles the
data and disables the recv(). This is because not all tasks are always
processed at once.

Instead of leaving the buffer free-wheeling and doing an EAGAIN, we
disable reading as soon as the first recv() succeeds. This way we're
sure that only the next wakeup of the task will re-enable it if needed.

Doing so has totally removed the EAGAIN we were seeing till now (30% of
recv).