Fix: incorrect time unit used when waiting on destruction handle

DEFAULT_DATA_AVAILABILITY_WAIT_TIME is used by the lttng client to
wait on the destruction handle returned by a session destruction
command. This constant is in micro-seconds while the destruction
handle expects a timeout in ms.

This causes the client to appear unresponsive while waiting for
the destruction of a session.

Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>