Replace systemd socket activation with old-style network interface configuration in config file. `CAP_NET_BIND_SERVICE` should be added during service startup and dropped once sockets are bound via `net.listen()` For more details, see discussion on mailing list: https://lists.nic.cz/pipermail/knot-resolver-users/2019/000182.html Related: #484 #342 #445 #### Related changes (preliminary plans) - [x] failing `net.listen()` should throw a lua error and therefore fail kresd if specified in configuration (by default) - [x] allow specifying `FREEBIND` in `net.listen()` - [x] unify TTY sockets, e.g. `net.listen('path', nil, { kind = 'control' })` - [x] add distro-specific preconfig (control socket location, cache size) - [x] use upgrade script to suggest updates to config and test in various envs