Instead of of our own private monitor socket, we send the
processed event back to our netlink socket, to the multicast
group 2 -- so any number of users can listen to udev events,
just like they can listen to kernel emitted events on group 1.
None of these rules is supposed to be changed by users, so move
them out of /etc. Custom rules, and automatically generated rules
stay in /etc. All rules are still processed in lexical order,
regardless which directory they live in.