Bluetooth: Do not trigger background scanning when HCI_AUTO_OFF is set

When a new controller is initialized, but not powered from userspace
at the moment, the HCI_AUTO_OFF flag is still set. During this period,
userspace might program device for auto-connection, but never power
on the controller. In this case do not try to start background
scanning and leave it for later to be started.

Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>