bluetooth: host: Do not try to set NRPA when scanning with identity

Attempting this would fail (assuming the controller is implemented
correctly) because when using legacy commands it is not allowed to
change the device address while scanning.

It also did not make sense. If we have configured the scanner to use
the identity address as own_addr, because the advertiser and scanner
addresses are shared when using legacy commands, setting the adv NRPA
here would overwrite the identity address used by the scanner, which
I assume is not the intention.

Signed-off-by: Olivier Lesage <olivier.lesage@nordicsemi.no>