Add reason code used to tell dialer when call failed due to WFC being off.

Adding new reason code which will be sent to Dialer to display a message
to the user when the call fails to the WFC being off.

Test: Manual
Bug: 28709116
Change-Id: I155fda9a47823d6d3f68be6f07dbe64998a582ae

telecomm/java/android/telecom/DisconnectCause.java

@@ -75,6 +75,14 @@ public final class DisconnectCause implements Parcelable {
      */
     public static final int CALL_PULLED = 12;
 
+    /**
+     * Reason code (returned via {@link #getReason()}) which indicates that a call could not be
+     * completed because the cellular radio is off or out of service, the device is connected to
+     * a wifi network, but the user has not enabled wifi calling.
+     * @hide
+     */
+    public static final String REASON_WIFI_ON_BUT_WFC_OFF = "REASON_WIFI_ON_BUT_WFC_OFF";
+
     private int mDisconnectCode;
     private CharSequence mDisconnectLabel;
     private CharSequence mDisconnectDescription;