Expose WifiConfiguration#ephemeral is a SystemApi

Bug: 34503179
Test: make
Change-Id: I3a89b89da67152bb522ae4dbfd1cfe1b4830d8ae

api/system-current.txt

@@ -27471,6 +27471,7 @@ package android.net.wifi {
     method public int describeContents();
     method public android.net.ProxyInfo getHttpProxy();
     method public boolean hasNoInternetAccess();
+    method public boolean isEphemeral();
     method public boolean isNoInternetAccessExpected();
     method public boolean isPasspoint();
     method public void setHttpProxy(android.net.ProxyInfo);

wifi/java/android/net/wifi/WifiConfiguration.java

@@ -707,6 +707,16 @@ public class WifiConfiguration implements Parcelable {
      */
     public boolean ephemeral;
 
+    /**
+     * @hide
+     * Indicate that a WifiConfiguration is temporary and should not be saved
+     * nor considered by AutoJoin.
+     */
+    @SystemApi
+    public boolean isEphemeral() {
+      return ephemeral;
+    }
+
     /**
      * @hide
      * A hint about whether or not the network represented by this WifiConfiguration