[AWARE] Fix visibility of Aware Characteristics API

Hide the get characteristics API - since the underlying characteristics
class is (still hidden). Will be opened in a separate phase from the parent
class.

Bug: 31912101
Test: update-api succeeded when opening the parent class
Change-Id: Ibe2f282027cd4b1c03bfb2b1e151551c34314541

wifi/java/android/net/wifi/aware/WifiAwareManager.java

@@ -304,6 +304,7 @@ public class WifiAwareManager {
      * limitations on configurations, e.g. the maximum service name length.
      *
      * @return An object specifying configuration limitations of Aware.
+     * @hide PROPOSED_AWARE_API
      */
     public WifiAwareCharacteristics getCharacteristics() {
         try {