Fill in DNS query type in DNS metric when DNS lookup hit cache

- When looking up DNS in cache, Rasta and DNS statistics are required
  Perform statistical analysis based on the type of DNS query.

The DNS stats proto shows "query type" as following:
============================================================
Without the commit:
        dns_query_events {
          dns_query_event {
            cache_hit: CS_FOUND
            latency_micros: 12
          }
With the commit:
        dns_query_events {
          dns_query_event {
            type: NS_T_AAAA <= ”DNS　query type”
            cache_hit: CS_FOUND
            latency_micros: 12
          }


Bug: 147031435
Test: statsd_testdrive
Change-Id: Iac6a6f819104247ecec65bb4134a33ddd66cfa9c