[DPP] Update javadoc for onFailure callback

Following up on API council feedback, update the javadoc for the
onFailure callback to explain the format of the channelListArray
sparse array.

Bug: 150685275
Test: No code changes.
Change-Id: I68e1cce89fa9dc50b79b41e2ca4e6d42a36d8aa2

wifi/java/android/net/wifi/EasyConnectStatusCallback.java

@@ -242,6 +242,8 @@ public abstract class EasyConnectStatusCallback {
      *                         to scan to find the network, see the "DPP Connection Status Object"
      *                         section in the specification for the format, and Table E-4 in
      *                         IEEE Std 802.11-2016 - Global operating classes for more details.
+     *                         The sparse array key is the Global Operating class, and the value
+     *                         is an integer array of Wi-Fi channels.
      * @param operatingClassArray Array of bands the Enrollee supports as expressed as the Global
      *                            Operating Class, see Table E-4 in IEEE Std 802.11-2016 - Global
      *                            operating classes.