Fix WPS docs for LABEL method

Since we don't support LABEL method in startWps, document
it explicitly.

Bug: 18298388

Change-Id: I5d4c2475a68f1b41e5fc449c911b7b01b3b82fc4
diff --git a/wifi/java/android/net/wifi/WifiManager.java b/wifi/java/android/net/wifi/WifiManager.java
index 1393bce..6ddebde 100644
--- a/wifi/java/android/net/wifi/WifiManager.java
+++ b/wifi/java/android/net/wifi/WifiManager.java
@@ -1968,7 +1968,7 @@
     /**
      * Start Wi-fi Protected Setup
      *
-     * @param config WPS configuration
+     * @param config WPS configuration (does not support {@link WpsInfo#LABEL})
      * @param listener for callbacks on success or failure. Can be null.
      * @throws IllegalStateException if the WifiManager instance needs to be
      * initialized again