MEDIUM: mux-quic: adjust timeout refresh

MEDIUM: mux-quic: adjust timeout refresh

Implement a new internal function qcc_refresh_timeout(). Its role will be
to reset QUIC MUX timeout depending if there is requests in progress or
not.

qcc_update_timeout() does not set a timeout if there is still attached
streams as in this case the upper layer is responsible to manage it.
Else it will activate the timeout depending on the connection current
status.

Timeout is refreshed on several locations : on stream detach and in I/O
handler and wake callback.

For the moment, only the default timeout is used (client or server). The
function may be expanded in the future to support more specific ones :
* http-keep-alive if connection is idle
* http-request when waiting for incomplete HTTP requests
* client/server-fin for graceful shutdown