Fix AudioFlinger TimeCheck

The conversion of IAudioFlinger to AIDL resulted in a regression in
its watchdog behavior. This change fixes that by allowing the
implementation to fully wrap the onTransact() call rather than just
prepend to it using onPreTransact().

Fixes: 187383878
Test: Added a long wait in createTrack, as described in the bug and
      watched to logs to confirm that the watchdog kills the process.
Change-Id: I3cceb2b37d27dbea2060ced3659e11bde363f86d