audio: allow enabling opus dtx, allow changing ptime (#1314)
audio: allow enabling opus dtx, allow changing ptime (#1314)

from the js console. Both are expert options with no gui

tired of waiting for travis. merging.

Co-authored-by: Harald Alvestrand <ce816cd73d80f958d82de1df356058c2d2bca378@google.com>
webrtc/samples,webrtc/samples