Add sanity check inside ServiceMonitor's setting observer.

When registering for a specific setting key uri, the observer
can also be called back for "parent uri" updates.  e.g.
adb shell content update --uri content://settings/secure will
trigger onChange with uri=content://settings/secure.

Add a quick setting value recheck, and avoid restarting if
the setting value change will have no impact.

Bug: 9595731
Change-Id: I4c71f6a4be3b655b31d2535e809bb42edd931cd6