Don't reject "ctl.stop.*" during shutdown.

We're shutting down anyway, so the service is either dead already
or about to be killed, and callers get upset (and don't have a good
response themselves) if we reject the request.

This was seen by a partner where adbd was asked to stop during
shutdown.

Bug: https://issuetracker.google.com/336223505
Change-Id: If09feeef2e0f2d1be9ff84a88cca6ed593a35362