Bluetooth: host: Ifdef starting of background scanner in init

Starting a background scanner for auto-connection is an API that is only
available when whitelist API is not enabled.
There is currently no way to set this bit when the whitelist API is
enabled so there is not any issues with the current code, but it is
still not correct.

Signed-off-by: Joakim Andersson <joakim.andersson@nordicsemi.no>