qdutils: idle_invalidator: Use fixed timeout rather than range

Currently the idle timeout is in a range from idle_timeout / 2
to idle_timeout, since we didn't need precise values.

Change this to a fixed value using timestamps, because the timeout
is too low and warrants precision.

Change-Id: I9cec1db7f1d7fda2996ab80449c61269915f6be4
3 files changed