Most DNS fails are caused by network issues, like connection timed out.
Lower log severity from error to warning to conform to go/greenlog.
Test: 1. connect to a WiFi AP without WAN
2. atest CtsNetTestCases:android.net.cts.DnsResolverTest
3. adb logcat | grep resNetworkResult:android
Bug: 181269159
Change-Id: Ifeaf250c91a4b9123d200bd62f085c11009f2491
5d1c4661da