Sort administrator UIDs for NetworkCapabilities.

Administrator UIDs stored in NetworkCapabilities should be sorted. This
allows for easier equals checks and hashCode computation. Additionally,
duplicate UIDs should be prevented.

Bug: 147903575
Test: atest FrameworksNetTests
Change-Id: Ia5387ca2ce7c3fcbd04dc7fbff5266f7bcc71694
Merged-In: Ia5387ca2ce7c3fcbd04dc7fbff5266f7bcc71694
(cherry picked from commit 2091bd90)