Add support for ipv6 PTR zones

[hno]

No description provided.

[benapetr]

Hello, I am really sorry for answering you so extremely late

This update on its own isn't going to work, that function HasPTRZones() is used to figure out whether logic for automatic adding (or removing) of PTR records should be enabled.

However the respective logic for doing that is supporting only IPv4 right now, so if this function enables the UI for automated PTR manipulation just because there are some IPv6 reverse zones it is just going to enable defunct UI elements, because the program is still not going to be able to automatically manipulate IPv6 records and user experience is going to be decreased.

The logic for automated PTR management is here:

• Adding - https://github.com/benapetr/dnsphpadmin/blob/master/includes/modify.php#L130
• Removing - https://github.com/benapetr/dnsphpadmin/blob/master/includes/modify.php#L177

Until these functions can handle IPv6 reverse zones, there is no point in that check returning true when IPv6 zone is found