Merge pull request #3654 from pi-hole/fix/ipv6_localhost_validator

Allow IPv6 loopback address to be added

automated install/basic-install.sh

@@ -1054,7 +1054,7 @@ valid_ip6() {
     # optional port number starting '#' with range of 1-65536
     local portelem="(#([1-9]|[1-8][0-9]|9[0-9]|[1-8][0-9]{2}|9[0-8][0-9]|99[0-9]|[1-8][0-9]{3}|9[0-8][0-9]{2}|99[0-8][0-9]|999[0-9]|[1-5][0-9]{4}|6[0-4][0-9]{3}|65[0-4][0-9]{2}|655[0-2][0-9]|6553[0-6]))?"
     # build a full regex string from the above parts
-    local regex="^(((${ipv6elem}))((:${ipv6elem}))*::((${ipv6elem}))*((:${ipv6elem}))*|((${ipv6elem}))((:${ipv6elem})){7})${v6cidr}${portelem}$"
+    local regex="^(((${ipv6elem}))*((:${ipv6elem}))*::((${ipv6elem}))*((:${ipv6elem}))*|((${ipv6elem}))((:${ipv6elem})){7})${v6cidr}${portelem}$"
 
     [[ ${ip} =~ ${regex} ]]