Fix background data clobbering other policies

Stop removing preexisting UID policies when toggling
Background network access / unrestricted data usage.

Fetching the state of policies was not working due to an incorrect use
of Arrays.asList() - if you give it an int array, you just get a list
with that int[] as a single element, so using the contains method with
an int will always return false. This has now all been refactored.

Test: Manual: Open Settings > Network & Internet > Data Saver >
Unrestricted data. Turn it on for something. Go back, and then
return to the page. It should still show as on.

Issue: calyxos#2547
Issue: calyxos#2118
Change-Id2: I671544f6fdf9897484c6265c31c8b3cd29ad4a92
Change-Id: If54d0a0925c5da0f3d519d0a85491ff3b7b62351