NETWORKING: Fix Portability of SO_LINGER=0 in Tests (elastic#33895)

* Setting SO_LINGER for open but not connected non-blocking sockets
throws on OSX
  * Fixed by only applying setting to connected sockets which will save
the same number of FDs as doing it on open sockets anyway
* closes elastic#33879

test/framework/src/main/java/org/elasticsearch/transport/nio/MockNioTransport.java

@@ -277,8 +277,9 @@ public void addCloseListener(ActionListener<Void> listener) {
 
         @Override
         public void setSoLinger(int value) throws IOException {
-            if (isOpen()) {
-                getRawChannel().setOption(StandardSocketOptions.SO_LINGER, value);
+            SocketChannel rawChannel = getRawChannel();
+            if (rawChannel.isConnected()) {
+                rawChannel.setOption(StandardSocketOptions.SO_LINGER, value);
             }
         }
 

test/framework/src/test/java/org/elasticsearch/transport/nio/SimpleMockNioTransportTests.java

@@ -19,7 +19,6 @@
 
 package org.elasticsearch.transport.nio;
 
-import org.apache.lucene.util.Constants;
 import org.elasticsearch.Version;
 import org.elasticsearch.cluster.node.DiscoveryNode;
 import org.elasticsearch.common.io.stream.NamedWriteableRegistry;
@@ -100,7 +99,6 @@ protected int channelsPerNodeConnection() {
     }
 
     public void testConnectException() throws UnknownHostException {
-        assumeFalse("Broken on Darwin - https://github.com/elastic/elasticsearch/issues/33879", Constants.MAC_OS_X);
         try {
             serviceA.connectToNode(new DiscoveryNode("C", new TransportAddress(InetAddress.getByName("localhost"), 9876),
                 emptyMap(), emptySet(),Version.CURRENT));