Bluetooth: Fix changing advertising random address when scanning

If active scan was started while advertising random adress was
set to NRPA. This results in device advertising with new adress
instead of RPA making it imposible to resolve its identity by
remote devices.

To fix this NRPA for active scan is set only if advertising is
not enabled. This resulst in RPA being used for scan requests
but this is OK since device is advertising anyway.

Change-Id: I35e98bee72f4abc033f5adc664698c14c5d8a2b0
Signed-off-by: Szymon Janc <ext.szymon.janc@tieto.com>