Right now if one wants to use the authentication radius rate-limit vendor option in L2TP and other accel-ppp services, they need to look up dictionary files in /usr/share/accel-ppp/radius and correctly guess which ones contain attributes useful for rate limiting.

Instead, we could provide completion for its built-in dictionaries (alcatel, cisco, microsoft, mikrotik) and add a validator to ensure that specified file exists, so that people can still use custom dictionaries if they want to.