SLAAC IPV6 addressing associated with Private reverse DNS servers not kept private when No hostname available.

### Issue Details

AdguardHome is using WHOIS by contacting the ISP to resolve client IPV6 Hostnames instead of using RDNS and relying on the local reverse lookup for ipv6 to discover client hostnames.
* **Version of AdGuard Home server:**
* Lastest Bleeding Edge (basically Master)
* **How did you install AdGuard Home:**
* Using AdguardHome provided Binaries directly
* **How did you setup DNS configuration:**
* AdguardHome is providing DNS directly on port 53, while DNSMASQ listens on a different upstream dns port while still providing DHCP service to clients. AdguardHome forwards Hostname lookup request to upstream DNSMASQ.
* **If it's a router or IoT, please write device model:**
* Asus RT-AX88U running Asuswrt-Merlin
* **CPU architecture:**
* aarch64
* **Operating system and version:**
* linux kernal 4.1.51 (busy box)
### Expected Behavior
I expected Adguard Home would be able to resolve hostnames for clients for both ipv4 and ipv6.
### Actual Behavior
AdguardHome does not resolve hostnames for ipv6 properly. It appears to be using WHOIS to obtain the ISP hostname from the upstream instead of honoring the reverse lookup option specified as a Private reverse DNS server reverse lookup options. If the Hostname for a SLAAC IPV6 address associated with a defined Private Reverse DNS Network cannot be found in the corresponding Private Reverse DNS server lookup, then the device hostname look up should not be passed off to WHOIS.
**here is another place this is mentioned**
https://github.com/AdguardTeam/AdGuardHome/discussions/2912#discussioncomment-1609475