Refix the MT call screen stuck issue.

The issue this change fixes can be reproduced by following steps:
1. Originate and connect a call to remote party #1 that is not in Contacts.
2. Receive a call from the remote party #2 that is not in Contacts, the
call waiting tone is sounded and the call waiting screen is displayed.
3. Press menu key and ignore the call, and the call waiting screen is
dismissed and the remote party #2 is forwarded to voice mail.
When we ignore the incoming call, Phone gets stuck with incoming call
screen.

The fix is to update the phone state before notifying the state change
in hangup() function.