Properly notify of precise call state change after connection hangup.

When disconnecting connections via Connection.hangup(), previously no
precise call state notification was sent out.
This change should fix BT headsets ringing indefinitely after a
blacklisted call came in, as BluetoothPhoneService can now update the
headset state properly.

Change-Id: I4439d7d8ed47e72da9d061b885ec9a0e6e1b784d