This is a bit problematic: libevdev only has one global log handler.
So if we have another driver use libevdev, we'll either overwrite that handler
or get overwritten, whichever comes first. So we need to re-set the handler
every time we get an event to make sure we log through our handler.
Likewise, if we ever drop the device, we need to unset the log handler back to
NULL because we may unload the module and our handler may disappear.

Use the lowest logging priority, let the server filter based on the verbosity
level instead.

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>