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binding an ipv6 address on an epoll channel when ipv6 is disabled "succeeds"

See original GitHub issue

Expected behavior

Trying to bind an IPv6 address if IPv6 is disable on the system should fail.

Actual behavior

The program silently binds the wrong port.

Steps to reproduce

Run the code below after sysctl net.ipv6.conf.all.disable_ipv6=0. When nio is used, the program fails with an expected exception:

Exception in thread "main" java.net.SocketException: Protocol family unavailable
	at sun.nio.ch.Net.bind0(Native Method)
	at sun.nio.ch.Net.bind(Net.java:433)
	at sun.nio.ch.Net.bind(Net.java:425)

When epoll is enabled, the program binds IPv4 0.0.0.1!

Minimal yet complete reproducer code (or URL to code)

import io.netty.bootstrap.ServerBootstrap;
import io.netty.channel.*;
import io.netty.channel.epoll.*;
import io.netty.channel.nio.*;
import io.netty.channel.socket.SocketChannel;
import io.netty.channel.socket.nio.*;
import java.net.InetSocketAddress;

public class Example {
  public static void main(String[] args) throws Exception {
    EventLoopGroup bossGroup;
    EventLoopGroup workerGroup;
    Class clazz;
    if (args.length > 1) {
      bossGroup = new EpollEventLoopGroup(1);
      workerGroup = new EpollEventLoopGroup();
      clazz = EpollServerSocketChannel.class;
    } else {
      bossGroup = new NioEventLoopGroup(1);
      workerGroup = new NioEventLoopGroup();
      clazz = NioServerSocketChannel.class;
    }

    ServerBootstrap b = new ServerBootstrap();
    b.group(bossGroup, workerGroup)
        .channel(clazz)
        .childHandler(
            new ChannelInitializer<SocketChannel>() {
              @Override
              public void initChannel(SocketChannel ch) throws Exception {}
            });

    ChannelFuture f = b.bind(new InetSocketAddress("[::1]", 0)).sync();
    f.channel().closeFuture().sync();
  }
}