Fixed mRestrictBackgroundWhitelistRevokedUids usage.

mRestrictBackgroundWhitelistRevokedUids used to be set on
removeRestrictBackgroundWhitelistedUidUL(), which has been refactored
into setUidPolicy().

Fixes: 28791717

Test: m -j32 FrameworksServicesTests && adb install -r -g ${ANDROID_PRODUCT_OUT}/data/app/FrameworksServicesTests/FrameworksServicesTests.apk && adb shell am instrument -e class "com.android.server.NetworkPolicyManagerServiceTest" -w "com.android.frameworks.servicestests/android.support.test.runner.AndroidJUnitRunner"

Change-Id: I097fddd236bf279890a8f466927fdc330360477f