Fix regression when trying to bind an EpollDatagramChannel with port (#10552)

only

Motivation:

4b7dba1 introduced a change which was not 100 % complete and so
introduce a regression when a user specified to use
InetProtocolFamily.IPv4 and trying to bind to a port (without specify
the ip).

Modifications:

- Fix regression by respect the InetProtocolFamily
- Add unit test

Result:

Fix regression when binding to port explicit

testsuite/src/main/java/io/netty/testsuite/transport/socket/DatagramUnicastTest.java

@@ -21,6 +21,7 @@ import io.netty.buffer.CompositeByteBuf;
 import io.netty.buffer.Unpooled;
 import io.netty.channel.Channel;
 import io.netty.channel.ChannelFuture;
+import io.netty.channel.ChannelHandlerAdapter;
 import io.netty.channel.ChannelHandlerContext;
 import io.netty.channel.ChannelInitializer;
 import io.netty.channel.ChannelOption;
@@ -50,6 +51,21 @@ public class DatagramUnicastTest extends AbstractDatagramTest {
         NONE, DUP, SLICE, READ_ONLY
     }
 
+    @Test
+    public void testBindWithPortOnly() throws Throwable {
+        run();
+    }
+
+    public void testBindWithPortOnly(Bootstrap sb, Bootstrap cb) throws Throwable {
+        Channel channel = null;
+        try {
+            cb.handler(new ChannelHandlerAdapter() { });
+            channel = cb.bind(0).sync().channel();
+        } finally {
+            closeChannel(channel);
+        }
+    }
+
     @Test
     public void testSimpleSendDirectByteBuf() throws Throwable {
         run();

transport-native-epoll/src/main/java/io/netty/channel/epoll/EpollDatagramChannel.java

@@ -276,8 +276,10 @@ public final class EpollDatagramChannel extends AbstractEpollChannel implements
         if (localAddress instanceof InetSocketAddress) {
             InetSocketAddress socketAddress = (InetSocketAddress) localAddress;
             if (socketAddress.getAddress().isAnyLocalAddress() &&
-                    socketAddress.getAddress() instanceof Inet4Address && Socket.isIPv6Preferred()) {
-                localAddress = new InetSocketAddress(LinuxSocket.INET6_ANY, socketAddress.getPort());
+                    socketAddress.getAddress() instanceof Inet4Address) {
+                if (socket.family() == InternetProtocolFamily.IPv6) {
+                    localAddress = new InetSocketAddress(LinuxSocket.INET6_ANY, socketAddress.getPort());
+                }
             }
         }
         super.doBind(localAddress);

transport-native-epoll/src/main/java/io/netty/channel/epoll/LinuxSocket.java

@@ -45,7 +45,7 @@ final class LinuxSocket extends Socket {
         super(fd);
     }
 
-    private InternetProtocolFamily family() {
+    InternetProtocolFamily family() {
         return ipv6 ? InternetProtocolFamily.IPv6 : InternetProtocolFamily.IPv4;
     }