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.

Fixes: 139110717
Test: toggle tethering, dumpsys network_stack version
Merged-In: I782f479de2d7d4c6579f206645a580c905009d85
(cherry picked from commit c6c1c69378)

Change-Id: I16b08e77351399d937b037c700b6e454b09f6d16

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;
     }
 }