DO NOT MERGE Use POSIX timer API for wake alarms instead of OSI callouts.

This change increases RFCOMM throughput by a little over 50%. We
were paying a pretty major cost in setting up / tearing down wake
timers by going through JNI and Binder over to AlarmService.

There are a few gotchas with this implementation, particularly
because the Linux kernel implementation of wake timers is somewhat
buggy.

Bug: 23375670
Change-Id: I27558f439e57696d912b968f56a48e5e4098860b