Finish moving NetworkStats tests to tests/net

Follow-up of commit 73fbb5303f3e4da9a8663478fe22438ff8819ac1.

Also add @SmallTest annotation to classes moved to tests/net.

Test: no functional change
Bug: 32561414
Change-Id: I0a0e8865d37ba7bae06ce352d3fc385989adc300
6 files changed
tree: 31adffe09c35117db5acee41d95123f792f0c723
  1. core/
  2. services/
  3. tests/