Added support for conference call SRVCC

1. Clear all handover connections that match state of CS connection
during SRVCC. This leads to the remaining DC calls take the route
of phantom call.

2. Fix the issue of Disconnected Connections not being removed from
ImsPhoneCall

Change-Id: I0268d511c6418d5a5a161e16f1e5bb3350b47868
CRs-Fixed: 756415