Call proper method to avoid waiting call going into hold state

With Current implementation, when there is active call, hold call
and waiting call, and if user answers waiting call, then below requests
are sent to RIL one after the other resulting in waiting call
moving to hold state instead of active state.
HANGUP_FOREGROUND_RESUME_BACKGROUND
REQUEST_SWITCH_WAITING_OR_HOLDING_AND_ACTIVE

Call answerAndEndActive method instead of answerCall when there are
already active call & hold call to avoid the issue. With this fix
only below request is sent to RIL and hence solves the issue.
HANGUP_FOREGROUND_RESUME_BACKGROUND

Change-Id: I83eac7f071ac95234357d83a16ee5ae58bc7e877
CRs-Fixed: 605531