Reject incoming call for a normal routing emergency call

An emergency call fails when receiving a call at the same time.

Case1. Reject incoming call when starting a normal routing emergency call.
Case2. Reject incoming call if it receives a new incoming call after
starting a normal routing emergency call.

Bug: 339159523
Test: atest EmergencyStateTrackerTest
Manual test:
1. Make a call from A to DUT.
2. Check whether the call is in alerting state in A.
3. At that moment, dial a normal routing emergency number in DUT
   before the incoming call is notified.

Change-Id: I42b4efbb075d4392064f2a177e4611d3257fcdcb