Bluetooth: Fix UUID/class mgmt command response synchronization

We should only return a mgmt command complete once all HCI commands to a
mgmt_set_dev_class or mgmt_add/remove_uuid command have completed. This
patch fixes the issue by having a proper async request complete callback
for these actions and responding to user space in the callback.

Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>
Acked-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>