Bluetooth: Move HCI_LIMITED_DISCOVERABLE changes to a general place

We'll soon be introducing also LE support for the Set Discoverable
management command, so move the HCI_LIMITED_DISCOVERABLE flag clearing
and setting out from the if-branch that is only used for a BR/EDR
specific HCI command.

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