This attribute specifies whether echo cancellation is performed on
this VoiceService. If echoCancellation is on, the internal echo
canceller is enabled and echo cancellation is performed. If
echoCancellation is off, the internal echo canceller is placed in
transparent bypass mode and echo cancellation is never performed.
If the echoCancellor or vtds feature is present, echoCancellation
defaults to on. Otherwise echoCancellation defaults to off.