Install: Check for valid upstream DNS IP addresses excludes IPv6 about pi-hole

[DL6ER]

Should be fixed by #5560

[voltagex]

Note that the UI once Pi-Hole is installed seems to work

[pralor-bot]

This issue has been mentioned on Pi-hole Userspace. There might be relevant details there:

https://discourse.pi-hole.net/t/setdns-in-basic-install-sh-does-not-support-ipv6-ipv6-upstream-dns-means-i-cant-finish-the-install/67890/1

[yubiuser]

Thanks for this report.

There are two issues here: one is expected and one is a bug.
Expected is that you need to overwrite the OS check - Trixi is not an supported OS.

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The IPv6 issue is a real bug. As you already found out, we need to check also for valid IPv6 addresses at

pi-hole/automated install/basic-install.sh

Line 978 in 19bfa08

if ! valid_ip "${PIHOLE_DNS_1}" || [[ ! "${PIHOLE_DNS_1}" ]]; then