This attribute specifies the time after the end of speech before
silence suppression starts. It applies only to voice traffic. It is not
used unless negotiatedIgSilenceSuppression is on, congested or
slowAndCongested.
Higher values of speechHangoverTime reduce undesirable clipping
but increase bandwidth usage.
speechHangoverTime is not used if this VoiceService is running on
a DS1V, E1V, 1pDS1V, 1pE1V or J2MV card.