Fix a bug where adding a user doesn't update network allow lists

Even if there are no preferences, the allow list needs
to be updated upon adding a new user, because it's set
unconditionally when the network connects.

Adding all existing UIDs would address this issue too
and we probably want to do it, but immediately this
seems simpler.

Bug: 266136779
Test: new test for this
Change-Id: I77091a6c3d3ccf2b80ab0aaa01d09ef0df922501
2 files changed