autotest: Add support for sending DNS responses to InterfaceHost

BUG=chromium:418738
TEST=A test using this is finally able to send responses back to Avahi.

Change-Id: Ib50a38fb039d20801cbe5b92b614c6d4e540f93f
Reviewed-on: https://chromium-review.googlesource.com/224260
Tested-by: Christopher Wiley <wiley@chromium.org>
Reviewed-by: Alex Deymo <deymo@chromium.org>
Commit-Queue: Christopher Wiley <wiley@chromium.org>
1 file changed