Change NetworkCapabilities administrator UIDs to be stored as int[].

NetworkCapabilities#mAdministratorUids is used to track the UIDs that
are administrators of the given Network. This value was previously
stored as List<Integer>. However, general Android API Council guidelines
recommend using Arrays for primitive values. In order to be consistent
with the guidelines, updating the field to use an Array.

Bug: 147903575
Test: atest FrameworksNetTests
Change-Id: I2652a5b0f276b8944454af5cb4b1383a3e054cfa