To suppress the mute function during an emergency call

During an emergency call, the mute function is suppressed on the call
screen UI, however the user can use mute function below.
- Add an emergency call after the user turns ON mute during
  a normal call
- Doing a long press the function button on the wired headset during
  an emergency call

With this fix, these use cases are suppressed.

Test: manual - Checked that the mute function is suppressed in each
use case
Test: auto - Passed BasicCallTests
Bug: 64102005

Change-Id: I271ef82ce8e96cf45954436f00b844926902d521