Add missing reset for expected address rotation time

When unregistering the last client, the expected address rotation time
were not reset. This generated a warning log (false alarm) when starting
a new scanning after unregistering all clients.

This CL only affects variables for logging purposes.

Bug: 344712454
Flag: EXEMPT, only affects logging
Test: m -j;
Test: Unregister scan client and start a new scan.
      The warning log is not printed.
Change-Id: I78f9154fdffd2e34de19cd55d1fef113bd3eac17