udev: try to reload selinux label database less frequently

udev: try to reload selinux label database less frequently

Previously, `event_run()` was called repeatedly in one `event_queue_start()`
invocation. Hence, the SELinux label database is reloaded many times needlessly.
Other settings, e.g. udev rules or hwdata, are tried to be reloaded in the
beginning of `event_queue_start()`. Let's also do so for the SELinux database.