Reduce the size of ns_query_t structure

The ns_query_t structure has a mechanism to check whether we are not in a recursion loop. Previously, the full qname and qdomain was stored in the structure as dns_fixedname_t which blew up the size of the ns_query_t by >= 512 bytes. Replace the two fixed names with full hashes of the qname and qdomain. This reduces the size of the recparam structure to roughly less than 20 bytes.