Include code when converting unknown causes to string

Bug: 17535687
Bug: 17241433
Change-Id: I12f0c3b4334dfcb5ac0cd2439ecab9dc77546680
diff --git a/telephony/java/android/telephony/DisconnectCause.java b/telephony/java/android/telephony/DisconnectCause.java
index 3fb6be7..6fe10dc 100644
--- a/telephony/java/android/telephony/DisconnectCause.java
+++ b/telephony/java/android/telephony/DisconnectCause.java
@@ -263,7 +263,7 @@
         case OUTGOING_CANCELED:
             return "OUTGOING_CANCELED";
         default:
-            return "INVALID";
+            return "INVALID: " + cause;
         }
     }
 }