Rename definitions and funtions of stats.

StatsRecords only include informations of dns servers. When adding the
information of Mdns statistics, we have to modifiy the names of server's
definitions and funtions to include mdns in stats files.

Bug: 140857615
Test: cd packages/modules/DnsResolver && atest
Change-Id: I38befe452d5d37b4172ee5dd16822083a08e4c88