Fix privileged apps calling registerDefaultNetworkCallback.

When registerDefaultNetworkCallback is called by an app that has
NETWORK_SETTINGS, the UID of the app is forgotten and the request
that is filed has an empty UID set. This results in that request
matching networks that have UID ranges that do not include it,
e.g., VPNs.

Fix this by ensuring that the UID ranges are properly set.

Bug: 165835257
Test: updated specific tests for this bug
Change-Id: I90bf79573342c144d1cfbc2f61a3155fdd5b1fa7