Ensure identifier disclosure windows survive modem restarts

A CellularIdentifierDisclosureNotifier may be enabled multiple times
in a row. Cases where this could happen are:

1. Multiple phone instances all call enable when the radio becomes
   available.
2. The radio becomes available multiple times during the lifetime of an
   active notifier, for instance, when the modem is restarting often.

Bug: 319662115
Test: atest CellularNetworkSecuritySafetySource
Change-Id: Id0460e6bcd7e764faf4bbab3180f41ca92a4ff33