Bluetooth: adv: add USE_NRPA advertising option

Allows the application to force the use of an NRPA.

This is applied regardless of any other roles running (ie scanner) or
advertising type.

Signed-off-by: Jonathan Rico <jonathan.rico@nordicsemi.no>
Co-authored-by: Aleksander Wasaznik <aleksander.wasaznik@nordicsemi.no>