Add asynchronous DNS query API and basic tests.

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/ runtest.sh
Change-Id: I98931cd561821cd396f8421e9419a289b371468a
4 files changed