MINOR: stream: Rely on a per-stream max connection retries value

MINOR: stream: Rely on a per-stream max connection retries value

Instead of directly relying on the backend parameter to limit the number of
connection retries, we now use a per-stream value. This value is by default
inherited from the backend value when it is set. So for now, there is no
change except the stream value is used instead of the backend value. But
thanks to this change, it will be possible to dynamically change this value.