Fix compile error introduced by bad cherry-pick of f7e8603d60

handler/src/test/java/io/netty/handler/flow/FlowControlHandlerTest.java

@@ -373,7 +373,7 @@ public class FlowControlHandlerTest {
         final Exchanger<Channel> peerRef = new Exchanger<Channel>();
         final CountDownLatch latch = new CountDownLatch(3);
         final AtomicReference<Throwable> causeRef = new AtomicReference<Throwable>();
-        ChannelInboundHandlerAdapter handler = new ChannelDuplexHandler() {
+        ChannelHandler handler = new ChannelHandler() {
             @Override
             public void channelActive(ChannelHandlerContext ctx) throws Exception {
                 ctx.fireChannelActive();