The add_advertising() and add_advertising_complete() functions reference
the now obsolete hdev->adv_instance struct. Both methods are being
refactored to access the dynamic advertising instance list instead.

This patch also introduces all logic necessary to actually deal with
multiple instance advertising. Notably the mgmt_adv_inst_expired() and
schedule_adv_inst() method are being referenced to schedule instances in
a round robin fashion.

This patch also introduces a "pending" flag into the adv_info struct.
This is necessary to identify and remove recently added advertising
instances when the HCI commands return with an error status code.
Otherwise new advertising instances could be leaked without properly
informing userspace about their existence.

Signed-off-by: Florian Grandel <fgrandel@gmail.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>