Add ipv6 support

[rhsCZ]

I managed to little modify install script for pihole5 to add support for ipv6 in nginx stream configuration. But i'm not sure if it will throw error when starting nginx if server hasn't ipv6 connection available or if is ipv6 disabled in system. Maybe needs more investigation or check for ipv6 connectivity in script. I can't do that right now because i write this from mobile.