Fix access point list jumping around in WifiSettings

This happens because the scan times are very aggressive
(to save power); and we don't find all APs on each scan.
So on each scan, some APs are considered lost and some
other are considered found; resulting in reordering the
list.

This change fixes that by requiring 3 scans to confirm
absence of an AP.

Bug: 7263326

Change-Id: I04f61ec5e5aa1589f457645acbf538c7e275a4bf