consumer: remove timeout for UST metadata

Remove time out for UST metadata by generating metadata packets whenever
they are about to be read from the ring buffer rather than filling them
when the metadata cache is updated, which requires a time out, and
therefore may fail.

Reviewed-by: Julien Desfossez <julien.desfossez@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>