Fix interfaceVersion in DhcpServerCallbacks

The getInterfaceVersion method was missed when freezing the AIDL
interface version.
This causes Q devices to return 0 instead of 3 on this interface.

Bug: 139110717
Test: toggle tethering, dumpsys network_stack version
Change-Id: If587cc9ead4191b9c2ad2ae65473bd89e7c37b5c

services/net/java/android/net/dhcp/DhcpServerCallbacks.java

@@ -21,13 +21,11 @@ package android.net.dhcp;
  * @hide
  */
 public abstract class DhcpServerCallbacks extends IDhcpServerCallbacks.Stub {
-    // TODO: add @Override here once the API is versioned
-
     /**
      * Get the version of the aidl interface implemented by the callbacks.
      */
+    @Override
     public int getInterfaceVersion() {
-        // TODO: return IDhcpServerCallbacks.VERSION;
-        return 0;
+        return IDhcpServerCallbacks.VERSION;
     }
 }