aaudio: pass strong pointers into threads

The AAudio service has several threads that are used
to handle routing changes (disconnects), and also the
timestamp generating thread.

In this CL we pass a strong pointer to the owning object into
the thread in order to prevent the object from being deleted
while the thread is running.

Bug: 179331032
Bug: 184774807
Test: atest CtsNativeMediaAAudioTestCases
Test: Run OboeTester "TEST DISCONNECTS" test.
Change-Id: I894f5c38fdf111257dea2bee9561c13608da52aa