Initial implementation of getRestrictBackgroundStatus() was just
handling the whitelist status of apps when data saver is turned on, but
when an app is blacklisted, it should return
RESTRICT_BACKGROUND_STATUS_ENABLED regardless of the data saver status.
BUG: 27432317
Change-Id: I5a027d8b7d17a13075510ff8f29d41eaa5a6beb8