[NAN] NAN System Api: RTT

Modify visibility of startRanging [NAN RTT] to SystemApi. Matches the
visibliity of the RttManager API.

Change-Id: Ia92de9885d0b38dfce74484f437bd122dd53cbf6
(cherry picked from commit ab9ef45971fc41bc078ad1362845309ef02f62f9)
diff --git a/wifi/java/android/net/wifi/nan/ConfigRequest.java b/wifi/java/android/net/wifi/nan/ConfigRequest.java
index 759098e..cd47359 100644
--- a/wifi/java/android/net/wifi/nan/ConfigRequest.java
+++ b/wifi/java/android/net/wifi/nan/ConfigRequest.java
@@ -16,6 +16,7 @@
 
 package android.net.wifi.nan;
 
+import android.annotation.SystemApi;
 import android.os.Parcel;
 import android.os.Parcelable;
 
diff --git a/wifi/java/android/net/wifi/nan/WifiNanManager.java b/wifi/java/android/net/wifi/nan/WifiNanManager.java
index a6e17af..7936518 100644
--- a/wifi/java/android/net/wifi/nan/WifiNanManager.java
+++ b/wifi/java/android/net/wifi/nan/WifiNanManager.java
@@ -21,6 +21,7 @@
 import android.annotation.Nullable;
 import android.annotation.SdkConstant;
 import android.annotation.SdkConstant.SdkConstantType;
+import android.annotation.SystemApi;
 import android.net.wifi.RttManager;
 import android.os.Binder;
 import android.os.Bundle;
diff --git a/wifi/java/android/net/wifi/nan/WifiNanSession.java b/wifi/java/android/net/wifi/nan/WifiNanSession.java
index ad9e7c3..8eb2f89 100644
--- a/wifi/java/android/net/wifi/nan/WifiNanSession.java
+++ b/wifi/java/android/net/wifi/nan/WifiNanSession.java
@@ -17,6 +17,7 @@
 package android.net.wifi.nan;
 
 import android.annotation.Nullable;
+import android.annotation.SystemApi;
 import android.net.wifi.RttManager;
 import android.util.Log;
 
@@ -167,7 +168,7 @@
      *                 {@link android.net.wifi.RttManager.RttParams#bssid} member must be set to
      *                 a peer ID - not to a MAC address.
      * @param listener The listener to receive the results of the ranging session.
-     * @hide (RTT API isn't public yet so can't unhide here)
+     * @hide PROPOSED_NAN_SYSTEM_API [TODO: b/28847998 - track RTT API & visilibity]
      */
     public void startRanging(RttManager.RttParams[] params, RttManager.RttListener listener) {
         if (mTerminated) {