Telecom: Retain LCH on conversation sub after remote hang up

After switching to other active sub due to remote hang up,
the LCH status of active sub is unset.

Retain LCH on conversation sub after remote hang up when
update LCH status and set mute, then if user clicks the
unmute button, the LCH status will be unset.

CRs-Fixed: 761742

Change-Id: I4e877e936d43e47c02c0ef12bad363c4a0ceaddc