Fix kotlin nullable errors that were exposed by setting the retention
of android.annotation.NonNull and android.annotation.Nullable to
class retention.
Bug: 294110802
Test: builds
Change-Id: Id49e4a2ee0b7b463d99bce6eb22919b84c21443a
Move the tests together with packages/Connectivity code, so both can be
moved to packages/modules/Connectivity together.
Also reorganize unit tests in a unit/ directory, as other tests
(integration/, common/ etc.) have been added in tests/net since they
were created. This makes the directory structure consistent.
Test: atest FrameworksNetTests
Bug: 187814163
Merged-In: I254ffd1c08ec058d594b4ea55cbae5505f8497cc
Change-Id: I254ffd1c08ec058d594b4ea55cbae5505f8497cc
