This has a potential bug that would need to be fixed in mtdev first:
if we get a SYN_DROPPED and we miss out on events, the current code emulates a
normal EV_SYN, feeds that to mtdev and hopes that that fills the mtdev output
queue.

If mtdev doesn't generate events on that EV_SYN, we're stuck in limbo and may
get weird results. The loop will continue and sync the device, but there's the
off chance we get odd events.

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>