mod_compat_roles: Fix attempt to index a nil value #1847 permissions[] is not a map with role names as keys since 817bc9873fc2 but instead a level with host names were added. This was likely an oversight. Refactored towards railroad.

This module helps make BOSH and WebSocket connection endpoints
discoverable via the HTTP method described in
[XEP-0156](https://xmpp.org/extensions/xep-0156.html#http).