[SPARK-24029][CORE] Follow up: set SO_REUSEADDR on the server socket.

"childOption" is for the remote connections, not for the server socket
that actually listens for incoming connections.

Author: Marcelo Vanzin <vanzin@cloudera.com>

Closes apache#21132 from vanzin/SPARK-24029.2.

Author: Marcelo Vanzin

common/network-common/src/main/java/org/apache/spark/network/server/TransportServer.java

@@ -99,8 +99,8 @@ private void init(String hostToBind, int portToBind) {
       .group(bossGroup, workerGroup)
       .channel(NettyUtils.getServerChannelClass(ioMode))
       .option(ChannelOption.ALLOCATOR, allocator)
-      .childOption(ChannelOption.ALLOCATOR, allocator)
-      .childOption(ChannelOption.SO_REUSEADDR, !SystemUtils.IS_OS_WINDOWS);
+      .option(ChannelOption.SO_REUSEADDR, !SystemUtils.IS_OS_WINDOWS)
+      .childOption(ChannelOption.ALLOCATOR, allocator);
 
     this.metrics = new NettyMemoryMetrics(
       allocator, conf.getModuleName() + "-server", conf);