AudioRecord locking

Fix race conditions for EVENT_MARKER and EVENT_NEW_POS callbacks.
Marker and new position update fields are protected by lock.

getSampleRate() doesn't need a lock because it reads from shared memory
control block.

Enforce that the parameter passed with EVENT_MARKER and EVENT_NEW_POS
cannot not be changed by the callback handler, and will not change during
the call by another thread.

Session ID should never change; log if it does.

Change-Id: Ia2c63cf1a71b10bb06c37981bd76437f83fffa91