Support additional records section in response

[alessionossa]

The records in the additional records section of DNS response are disregarded.

The specifications of this sections are in https://www.ietf.org/rfc/rfc1035.txt.

Regarding c-ares, the current version is 1.19.1. In version 1.21.0, however, the logic that parse DNS responses has been been rewritten, introducing support for the additional records section. Specifically, to support this, the following has been suggested:

ares_dns_parse() will parse all records, and additional section records can be retrieved with ares_dns_record_rr_get(..., ARES_SECTION_ADDITIONAL, ...)

https://c-ares.org/docs/ares_dns_parse.html
https://c-ares.org/docs/ares_dns_rr.html

Hint: use ares_send_dnsrec(), ares_query_dnsrec(), or ares_search_dnsrec() to retrieve the already-parsed dns record pointer in the c-ares callback.