Retrieve the res_stats based on a given list of nameserver addresses

Similar to aosp/1136436, each independent lookup thread should get
the stats based on its own nameserver address list rather than the
list stored in NetConfig.

With this change, plus aosp/1136436, it's able to populate nameserver
addresses in random order to lookup threads without the worry of
breaking the legacy stats stored in NetConfig.

Bug: 137169582
Test: cd packages/modules/DnsResolver && atest
Change-Id: I8d5c639326d2931bf7e5f5ae668e7aba830e00fb