dns: consolidate reverse zone files (part 1)
- The current implementation uses the smallest prefix defined in Netbox for any given address to generate a zonefile per prefix for reverse DNS records. This generates too many files that will require to be $INCLUDEd one by one manually in the DNS repo.
- Relax the selection of the prefix to consolidate more the reverse zone files. In particular:
- If the IP has a preifx lenght > 29 look for the first parent prefix that has a prefixlen <= 29 and use that one to generate the zonefile name.
- Keep the existing records as they were before for a smoother transition. In part 2 they will be removed after all the $INCLUDEs have been migrated to the consolidated files.