[sr-dev] [kamailio/kamailio] absolute dns names trigger error (#2706)

[sergey-safarov]

In one config I use
```
dns_cache_flags = 4
dns_cache_init = off
```

Looks as when Kamailio try to resolve DNS hostname sended two DNS requests:
1. A for IPv4 address resolving;
2. AAAA for IPv6 address resolving.

When DNS hostname has only AAAA record and do not has A record, then
1. AAAA request will be successful;
2. A request will return `NXDomain`.

Looks as when Kamailio received `NXDomain`, then takes the server hostname domain and adds this part to searched DNS name and repeated request.
Example:
1. I need to send a packet to `ipv6.test-ipv6.com` that has only AAAA dns record.
2. Kamailio hostname `proxy.example.com`;
3. Kamailio send `ipv6.test-ipv6.com` AAAA request, successful;
4. Kamailio send `ipv6.test-ipv6.com` A request, `NXDomain`;
3. Kamailio send `ipv6.test-ipv6.com.example.com` AAAA request, `NXDomain`;
4. Kamailio send `ipv6.test-ipv6.com.example.com` A request, `NXDomain`.

Using absolute DNS name, I want Kamailio to not modify DNS name and not send extra requests.

Tested on master.

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