Fix time measurement in FilterDelayHintTest

The startTime needs to be set before setting the delayHint timeout as
that is when the callback scheduler's clock start ticking.

In addition, we need to await the first callback before starting the
test to make sure the scheduler thread has been run at least once (so
the timeout should be initialized correctly).

Test: atest TunerFilterAidlTest#FilterDelayHintTest
Bug: 210943300
Change-Id: I0b2443f3e7d33977fb6666ba09d3ff51d8b1f152