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 lets you block connections to any remote servers not on a
whitelist.

``` {.lua}
modules_enabled = {
    -- other modules --
    "s2s_whitelist",

}
s2s_whitelist = {
    "example.org",
}
```