Expose only ConnectionFactory#netty() to activate Netty

Having a method like useNetty() is not necessary as netty() activates
Netty as well. Moreover useNetty() does not allow to set the
EventLoopGroup, which is essential to configure when using Netty.

References #1663

Author: acogoluegnes

src/main/java/com/rabbitmq/client/ConnectionFactory.java

@@ -1883,14 +1883,7 @@ public ConnectionFactory setTrafficListener(TrafficListener trafficListener) {
     return this;
   }
 
-  /**
-   * Use Netty with the default configuration.
-   *
-   * @return the connection factory
-   * @see #netty()
-   * @since 5.27.0
-   */
-  public ConnectionFactory useNetty() {
+  private ConnectionFactory useNetty() {
     this.netty = true;
     this.nio = false;
     return this;

src/test/java/com/rabbitmq/client/test/NettyTest.java

@@ -51,7 +51,7 @@ public class NettyTest {
   @BeforeEach
   void init() {
     cf = TestUtils.connectionFactory();
-    cf.useNetty();
+    TestUtils.setIoLayer(cf, TestUtils.IO_NETTY);
   }
 
   @Test

src/test/java/com/rabbitmq/client/test/TestUtils.java

@@ -52,7 +52,7 @@ public class TestUtils {
   public static final String IO_LAYER = System.getProperty("io.layer", "netty");
   private static final String IO_SOCKET = "socket";
   private static final String IO_NIO = "nio";
-  private static final String IO_NETTY = "netty";
+  public static final String IO_NETTY = "netty";
   public static final List<String> IO_LAYERS =
       Collections.unmodifiableList(Arrays.asList(IO_SOCKET, IO_NIO, IO_NETTY));
 
@@ -103,7 +103,7 @@ public static void setIoLayer(ConnectionFactory cf, String layer) {
     if (isNio(layer)) {
       cf.useNio();
     } else if (isNetty(layer)) {
-      cf.useNetty();
+      cf.netty();
     } else if (isSocket(layer)) {
       cf.useBlockingIo();
     } else {