MINOR: dns: make 'ancount' field to match the number of saved records

MINOR: dns: make 'ancount' field to match the number of saved records

ancount is the number of answers available in a DNS response.
Before this patch, HAProxy used to store the ancount found in the buffer
(sent by the DNS server).
Unfortunately, this is now inaccurate and does not correspond to the
number of records effectively stored in our local version of the
response. In Example, the CNAMEs are not stored.

This patch updates ancount field in to make it match what is effectively
stored in our version.