audioflinger: fix FIXME in logBufferSizeUnderruns

Some debug code was accidentally merged.
The hang was caused by a recursive lock of mLock.
The code now calls lockfree methods.
Added events for RELEASE and SETBUFFERSIZE.

Bug: 157916126
Test: adb logcat | grep logBufferSize
Test: launch OboeTester
Test: disable MMAP checkbox
Test: Tap OPEN and START
Test: move bufferSize fader
Test: expect to see no spam from logBufferSizeInFrames()
Test: adb shell dumpsys media.metrics
Test: expect to see entries like "(bufferSizeFrames=118, underrun=1)"
Change-Id: I7d782ccea2c2470bc18a3a61cfb8767430a441d8