Bluetooth: Refactor set_connectable settings update to separate function

We will need to directly update the device flags and notify user space
of the new settings not just when we're powered off but also if it turns
out that there are no HCI commands to send (which can happen in
particular when BR/EDR is disabled). Since this is a considerable amount
of code, refactor it to a separate function so it can be reused for the
"no HCI commands to send" case.

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