Update API documentation for onRttInitiationFailure.

Add intdef for reason code.
Clarifying when this callback can be expected and how to handle RTT
state when requested at the start of a call.

Test: Docs only change
Bug: 216608696
Change-Id: I86e46fbb2b0693564a41d1ca0d9f8c180d775c1a
diff --git a/telecomm/java/android/telecom/Call.java b/telecomm/java/android/telecom/Call.java
index d94fafc..980ea5c 100644
--- a/telecomm/java/android/telecom/Call.java
+++ b/telecomm/java/android/telecom/Call.java
@@ -1476,12 +1476,21 @@
         /**
          * Invoked when the RTT session failed to initiate for some reason, including rejection
          * by the remote party.
+         * <p>
+         * This callback will ONLY be invoked to report a failure related to a user initiated
+         * session modification request (i.e. {@link Call#sendRttRequest()}).
+         * <p>
+         * If a call is initiated with {@link TelecomManager#EXTRA_START_CALL_WITH_RTT} specified,
+         * the availability of RTT can be determined by checking {@link Details#PROPERTY_RTT}
+         * once the call enters state {@link Details#STATE_ACTIVE}.
+         *
          * @param call The call which the RTT initiation failure occurred on.
          * @param reason One of the status codes defined in
-         *               {@link android.telecom.Connection.RttModifyStatus}, with the exception of
-         *               {@link android.telecom.Connection.RttModifyStatus#SESSION_MODIFY_REQUEST_SUCCESS}.
+         *      {@link android.telecom.Connection.RttModifyStatus}, with the exception of
+         *      {@link android.telecom.Connection.RttModifyStatus#SESSION_MODIFY_REQUEST_SUCCESS}.
          */
-        public void onRttInitiationFailure(Call call, int reason) {}
+        public void onRttInitiationFailure(Call call,
+                @android.telecom.Connection.RttModifyStatus.RttSessionModifyStatus int reason) {}
 
         /**
          * Invoked when Call handover from one {@link PhoneAccount} to other {@link PhoneAccount}