start xow.service on dongle plugin

[atcq]

I encountered the Mt76Exception: Failed to load firmware error quite a few times. xow.service is stopped and needs a restart as stated in the Troubleshooting section of the README.md. To make my life easier i added a udev rule to do just that for me when i plugged the dongle back in after unplugging it. Should start/restart the xow.service if the service is not running or is in a failed state due to previous ABRT signal. I think it would be a simple change to the udev.rules to make that the default behaviour but maybe a manual restart is desired?

Anyways, i hope i did this the right way with a pull request and thanks a lot for your work! I'm quite happy with xow!