fix(coolwsd): listen on loopback only

[joshtrichards]

Fixes #340

[khoschi]

Well, yes, but actually no.
Good news:
With the fix and the setting "127.0.0.1/8,::1/128" in the admin panel the listening changes to "tcp6 0 0 ::1:9983" in netstat, so it binds to loopback only. Safe!
Bad news:
It will stop working at all, as nextcloud refuses to connect. So ps shows what is going on:
--o:net.listen=loopback
--o:net.lok_allow.host[14]='DNS NAME' (pipe)
--o:remote_font_config.url='https://DNS NAME/apps/richdocuments/settings/fonts.json'
--o:net.lok_allow.host[14]='DNS NAME' (again)

The external DNS hostname shows up, but is unreachable with the fix. DNS NAME should read localhost or localhost.localdomain, but I have no idea what else breaks if I would enter that - most webservers do not deliver the same content and URL scheme under this hostname (even if - cert names do not mach with SSL).

Anyway, the font block at the bottom of nextcloud settings page won't load, probaly this is connected.