Add asynchronous DNS query API

Adds support for asynchronous "raw" DNS API for clients.
API allows apps to use multinetworking capability correctly
and also allows other query types than A/AAAA.

Test: built, flashed, booted
      cts test: NativeDnsAsyncTest

Change-Id: I4701b76bd8f0094ef1bdd7c5371b54387914a91b