Settings: fix up advanced mode logic

The overlay config value should be a 'always-on' switch, otherwise
we should read the user-set setting.

Advanced mode should always be off by default.

Ref: CYNGNOS-815

Change-Id: I7f66eaf7fc84e9d3842e4ae874ffba2050b89ea6
Signed-off-by: Roman Birg <roman@cyngn.com>
(cherry picked from commit 055e70f6)