Clear dns cache when restoring network access

Sometimes apps need to wait for network rules to be updated before some
of their lifecycle events can be dispatched. This happens specifically
before resuming activities today.

Because the process-level InetAddress library can cache dns failures,
we need to clear its cache so that the app can resume making valid dns
queries as soon as any of its activities resume.

Test: Manual

Bug: 237556596
Change-Id: Ia99a43731801078ec8d67cf17fbfee9c329b6e96