[Monocle] key events on udev input path don't work correctly on odroid

If you run monocle-egl/x11 on the odroid and use the udev input path (default), key events aren't working properly. It appears we aren't handling the case where keys come in "out of order", so to speak, for example:

press a
press b
release a
release b

In the case above, we just drop the b (and anything else that comes in between the press a and release a).