Handle call termination in midst of call switching

When one of the calls gets disconnected in the midst of call switching,
we need to put the remaining call back into active state.
There are a couple of scenarios that could arise which needs to be
handled:
1. The call which was supposed to become ACTIVE (and hence foreground)
gets disconnected in the midst of switch.
2. The call which was supposed to be HELD (and hence background) gets
disconnected in the midst of switch.

To handle the above 2 scenarios in the midst of a switch:
1. We need to swap back the foreground/background call if the call
expected to resume is the one that was terminated.
2. Put the foreground call to active if it is in HOLDING state and we
find that the background call is terminated in the midst of a switch.

BUG: 24066890
Change-Id: I75d41c123166be42cfc166eb3ed5e7629235c297