New comment by Hoshpak on void-packages repository

https://github.com/void-linux/void-packages/issues/14440#issuecomment-531473672

Comment:
Indeed, I tried on my second Void installation and it had /dev/kvm set to 0666 after a system boot. It was probably libvirt on my first installation that touched the device that touched the device and thus lead to udev setting the correct permissions.

I experimented a bit with it and if I comment out the udev default rule, the permissions get applied correctly. If I remove both rules, the default is root:root and 0600. Not really finding an explanation why the second rule seems to be ignored on boot I thought it might be because the first one is more specific and the rules don't match exactly. I'm still not sure if that is the cause but either removing `OPTIONS+="static_node=kvm"` from the first rule oder adding it to the second rule leads to both rules being executed during udev startup and it works as expected.  

While we could just patch the udev default rules, I think it would be better to change the base-files rule so the default one gets properly overridden.