Add comment of using same callback for start/stop advertising.

Change-Id: Ice268e83e4f2ceb5053a0e03f73b877f548bd13b
diff --git a/core/java/android/bluetooth/BluetoothAdapter.java b/core/java/android/bluetooth/BluetoothAdapter.java
index 75b007c..229bcbf 100644
--- a/core/java/android/bluetooth/BluetoothAdapter.java
+++ b/core/java/android/bluetooth/BluetoothAdapter.java
@@ -570,7 +570,7 @@
     }
 
     /**
-     * Stop BLE advertising.
+     * Stop BLE advertising. The callback has to be the same one used for start advertising.
      *
      * @param callback - {@link AdvertiseCallback}
      * @return true if BLE advertising stops, false otherwise.