Fix setInterfaceEnabled method signature

- Mark setInterfaceEnabled as public as it is called from
  EthernetServiceImpl.
- Mark EthernetCallback as NonNull.
- Remove final qualifiers as they have no meaning to the caller and make
  the code harder to read (by introducing line breaks).

Test: TH
Change-Id: I9f030e8c40938e5f1e9ad0a32313828eeea4fdd3
diff --git a/service-t/src/com/android/server/ethernet/EthernetTracker.java b/service-t/src/com/android/server/ethernet/EthernetTracker.java
index 458d64f..8fb632e 100644
--- a/service-t/src/com/android/server/ethernet/EthernetTracker.java
+++ b/service-t/src/com/android/server/ethernet/EthernetTracker.java
@@ -382,9 +382,8 @@
         });
     }
 
-    @VisibleForTesting(visibility = PACKAGE)
-    protected void setInterfaceEnabled(@NonNull final String iface, boolean enabled,
-            @Nullable final EthernetCallback cb) {
+    /** Configure the administrative state of ethernet interface by toggling IFF_UP. */
+    public void setInterfaceEnabled(String iface, boolean enabled, EthernetCallback cb) {
         mHandler.post(() -> updateInterfaceState(iface, enabled, cb));
     }