Take all VPN underlying networks into account when migrating traffic for

VPN uid.

(cherry picked from commit 95aa6d44)

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