Fix IMS Emergency Callback Mode issues

1. ECM timer doesn't resume after user hangs up another emergency call
during IMS ECM. Therefore, user can't exit ECM except by phone reboot or
making volte call.

2. User can't enable mobile data if user disable mobile data during IMS
ECM.

To fix the problem:
1. In ImsPhoneCallTracker.java, implement restarting ECM timer when
removing connection like GsmCdmaCallTracker.java

2. In DcTracker.java, added condition to allow mobile data during IMS
ECM.

Test: manual - Verified that ECM timer is restarted after 2nd emergency
call is disconnected.
Bug: 141287026

Change-Id: Id684a8b67149114db6944569f3c03234411e75d1