MINOR: resolvers: renames some resolvers internal types and removes dns prefix

Some types are specific to resolver code and a renamed using
the 'resolv' prefix instead 'dns'.

-struct dns_query_item {
+struct resolv_query_item {

-struct dns_answer_item {
+struct resolv_answer_item {

-struct dns_response_packet {
+struct resolv_response {
3 files changed