mod_turn_external: Fix type of config option (thanks mirux) There was a separate boolean option to enable TLS before, but it was merged with the port number option and it seems the typed API interface got confused. Backport of trunk rev aa7a8aa64d3f

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

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