Use more precise neighboring cell mode

[coderbyheart]

Currently it is hard-coded at build time. Allow run-time configuring the search mode.

[maxd-nordic]

Which KConfig option do you mean?

[coderbyheart]

I don't think there is a KConfig option right now to control the mode. It's hard coded.

[coderbyheart]

With this PR the search "depth" can be configured at run-time: nrfconnect/sdk-nrf#11549

Add a config property that allows to change it.