Replace addrinfo with IPSockAddr to store dns addresses

The struct addrinfo is designed to store multi-addresses and it
might cause memory leaks if improperly used. IPSockAddr is safer
and is extensible. It also helps simplify the struct resolv_cache_info,
where nameservers and nscount is no longer necessary.

Bug: 130686826
Test: atest --include-subdirs packages/modules/DnsResolver
Change-Id: I3243f2f79c94ebe3d03503914d25b5863da20c09