Subscribe to notifications when creating a notif. iterator

Subscribe to notifications when creating a notif. iterator

bt_private_connection_create_notification_iterator() now accepts a new
parameter which is a BT_NOTIFICATION_TYPE_SENTINEL-terminated array of
notification types to subscribe to. It is guaranteed that, after any
bt_notification_iterator_next() called on the created iterator (if the
status is BT_NOTIFICATION_ITERATOR_STATUS_OK), the following call to
bt_notification_iterator_get_notification() returns a notification to
which the iterator is subscribed.

You can pass NULL to the notification types parameter of
bt_private_connection_create_notification_iterator() to subscribe to all
existing notifications (including the ones that will be added to the
following versions of the library).

The use case behind the subscription mechanism is for a notification
iterator to avoid the generation of automatic notifications when the
iterator's user does not expect them anyway. This should be the case of
some filters and sinks, text.pretty being a current example (only needs
event notifications).

Tests and existing plugins are updated accordingly.

Signed-off-by: Philippe Proulx <eeppeliteloop@gmail.com>
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>