aaudio: fix race condition in requestStart()

Set callback enable flag before starting AudioTrack callback.

Bug: 72115512
Test: Repeat:  adb shell write_sine_callback -pn -s4
Test: 20 times and make sure framesWritten is advancing.
Change-Id: I670fde46da0dccf8a6d03478fe2aa8b7ad596a3b
4 files changed