Take all VPN underlying networks into account when migrating traffic for

VPN uid.

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: I9d8d0cc58d18002c1c96f8ddff780ef8dc452d21