WifiManager: Add new API to restore old backup data

Add a new API to restore the old backups containing the raw data from
wpa_supplicant.conf & ipconfig.txt files.
This helps clean up all the existing wifi configuration parsing
logic from SettingsBackupAgent.

BUG: 29075035
Change-Id: I8c7b93ef7c9e2decc8e4f9e5d7038939cf0ef196

wifi/java/android/net/wifi/IWifiManager.aidl

@@ -173,5 +173,7 @@ interface IWifiManager
     byte[] retrieveBackupData();
 
     void restoreBackupData(in byte[] data);
+
+    void restoreSupplicantBackupData(in byte[] supplicantData, in byte[] ipConfigData);
 }
 

wifi/java/android/net/wifi/WifiManager.java

@@ -2761,4 +2761,17 @@ public class WifiManager {
             throw e.rethrowFromSystemServer();
         }
     }
+
+    /**
+     * Restore state from the older version of back up data.
+     * The old backup data was essentially a backup of wpa_supplicant.conf & ipconfig.txt file.
+     * @hide
+     */
+    public void restoreSupplicantBackupData(byte[] supplicantData, byte[] ipConfigData) {
+        try {
+            mService.restoreSupplicantBackupData(supplicantData, ipConfigData);
+        } catch (RemoteException e) {
+            throw e.rethrowFromSystemServer();
+        }
+    }
 }