BT-HF: Disconnect SCO when MT call received while VR active.

When a MT call is received while VR is active, although
stopVoiceRecognition() is called, but BT app doesn't disconnect
SCO. Check for MT call state and allow disconnectAudioNative.

CRs-Fixed: 705954

Change-Id: I11604bcc6dcfe2d2758c4d88db5bf27280592837