Migrate from network isolation to restricted networking mode

* Pre-12, we used to implement network-isolation with POLICY_REJECT_ALL
* Starting from 12, we've switched to AOSP's restricted-networking-mode
* Read uids which were isolated, and migrate them to restricted networking,
  for both upgrades (which may be from 11) and restores (same)
* Remove POLICY_REJECT_ALL for migrated uids to avoid future conflicts

Co-authored-by: Chirayu Desai <chirayudesai1@gmail.com>
Change-Id: I01d21abb9084eb1f61ccefd8a6da33e82697294e