[Security Report] Fix Settings WifiScanModeActivity Overlaid issue

- Disallowed non system overlay windows

- Screenshot
  https://screenshot.googleplex.com/77fJ9QN6pV4zFYc

Bug: 174047492
Test: manual test

Merged-In: Ia7acad6d456ce5ebea2d982d4cb063d4f28cbfff
Change-Id: Ia7acad6d456ce5ebea2d982d4cb063d4f28cbfff
(cherry picked from commit d47d8e4f)