dns_core: Create new API ast_dns_resolve_ipv6_and_ipv4

The new function takes in a pointer to an ast_sockaddr structure,
a hostname and an optional port and then dispatches parallel
"AAAA" and "A" record queries.  If an "AAAA" record is returned,
it's parsed into the ast_sockaddr structure along with the port
if it was supplied.  If no "AAAA" record was returned, the
first "A" record returned (if any) is parsed instead.

This is a synchronous call.  If you need asynchronous lookups,
use ast_dns_query_set_resolve_async and roll your own.

Change-Id: I194b0b0e73da94b35cc35263a868ffac3a8d0a95