Only apply VPN isolation if it's fully routed

VPN is considered fully routed if both IPv4 and IPv6 have
either a default route or a prohibit route.

Bug: 145332510
Test: atest FrameworksNetTests
Change-Id: I59cf48552bca98092d1212e3d718fd420add5458
6 files changed
tree: 04aebe6d230b41f8c8831b75f0e161b3a722c11b
  1. core/
  2. services/
  3. tests/