aaudio: prevent deadlock when stop() calls disconnect()

Move all calls to send the timestamp into the one timestamp thread.

There was a clear code path that could lead to a deadlock.
If the call to get the timestamp from the HAL returned
an unexpected error code then it would call disconnect().
If that happened below the call to stop() then the
deadlock would occur.

The sequence of calls was AAudioServiceStreamBase::stop()
  which locked mLock,
  then called AAudioServiceStreamBase::stop_l(),
  which called AAudioServiceStreamBase:sendCurrentTimeStamp(),
  which called AAudioServiceStreamMMAP::getFreeRunningPosition(),
  which called disconnect(),
  which locked mLock AGAIN.

It is not clear what would trigger the error return
from the HAL but a routing change may be involved.

The bug was discovered during stress tests and we do not
have a clear repro case.

Bug: 182852602
Test: atest CtsNativeMediaAAudioTestCases
Change-Id: I575f75ece9b459e7412bca293d7338babe76b3a7