VPN uid.
(cherry picked from commit c8dbdf35de)
Bug: 113122541
Bug: 120145746
Test: atest FrameworksNetTests
Test: Manually verified on device that stats from VPN UID are moved
appropriately based on its declared underlying network set.
Test: vogar --mode app_process --benchmark NetworkStatsBenchmark.java
Change-Id: I7f368c5970b2dcb969fe0daf5ef44edb1f51d09d