Cleanup the StateMachine thread during RilMessageDecoder dispose.

Currently the dispose() method in RilMessageDecoder wont stop the
state machine thread, and each time a new state Machine thread is
created which causes the file descriptor leakage.

Add quitNow() method  in dispose() of RilMessageDecoder to stop the
state machine thread.

bug:22992703
Change-Id: I83f773adf7f5fc0b82abf912f2db7fec8a0aa87b