Split lldp migration up

- account_* tables are not available at the time the service migration
  is run. While this works for a running system, it doesn't work on
  fresh installs. If there is a better way to do this, do it ;-)
- In order to make this work on an existing system with the lldp migration
  already in place, I had to remove the entries in the account_bsdusers
  and account_bsdgroups tables for the ladvd user, and drop the
  services_lldp table. I don't consider this a bug since it won't happen
  to those who did not run the migration already.