Fix: wait parameter in UST request metadata

Depending on the call site, we don't necessarily want to wait for all
the metadata to be flushed in the channel, this patch adds a parameter
to control this feature and give more control to the caller.

Signed-off-by: Julien Desfossez <jdesfossez@efficios.com>
Commit metadata packet to the channel and retry

Signed-off-by: Julien Desfossez <jdesfossez@efficios.com>
nest rdv_lock in stream lock

Signed-off-by: Julien Desfossez <jdesfossez@efficios.com>
[MERGE] fix commit one metadata packet returned value check

Signed-off-by: David Goulet <dgoulet@efficios.com>