Fix potential race during TcpTransport close (#39031)

Fixed two potential causes for leaked threads during tests:
1. When adding a channel to serverChannels, we add it under a monitor
that we do not use when reading from it. This is potentially unsafe if
there is no other happens-before relationship ensuring the safety of
this.
2. Long-shot but if the thread pool was shutdown before entering this
code, we would silently forget about closing server channels so added
assert.

Strengthened the locking to ensure that once we stop the transport, no
new server channels can be made.

Relates to CI failure issue: #37543

server/src/main/java/org/elasticsearch/transport/TcpTransport.java

@@ -388,28 +388,28 @@ private InetSocketAddress bindToPort(final String name, final InetAddress hostAd
         PortsRange portsRange = new PortsRange(port);
         final AtomicReference<Exception> lastException = new AtomicReference<>();
         final AtomicReference<InetSocketAddress> boundSocket = new AtomicReference<>();
-        boolean success = portsRange.iterate(portNumber -> {
-            try {
-                TcpServerChannel channel = bind(name, new InetSocketAddress(hostAddress, portNumber));
-                synchronized (serverChannels) {
-                    List<TcpServerChannel> list = serverChannels.get(name);
-                    if (list == null) {
-                        list = new ArrayList<>();
-                        serverChannels.put(name, list);
-                    }
-                    list.add(channel);
+        closeLock.writeLock().lock();
+        try {
+            if (lifecycle.initialized() == false && lifecycle.started() == false) {
+                throw new IllegalStateException("transport has been stopped");
+            }
+            boolean success = portsRange.iterate(portNumber -> {
+                try {
+                    TcpServerChannel channel = bind(name, new InetSocketAddress(hostAddress, portNumber));
+                    serverChannels.computeIfAbsent(name, k -> new ArrayList<>()).add(channel);
                     boundSocket.set(channel.getLocalAddress());
+                } catch (Exception e) {
+                    lastException.set(e);
+                    return false;
                 }
-            } catch (Exception e) {
-                lastException.set(e);
-                return false;
+                return true;
+            });
+            if (!success) {
+                throw new BindTransportException("Failed to bind to [" + port + "]", lastException.get());
             }
-            return true;
-        });
-        if (!success) {
-            throw new BindTransportException("Failed to bind to [" + port + "]", lastException.get());
+        } finally {
+            closeLock.writeLock().unlock();
         }
-
         if (logger.isDebugEnabled()) {
             logger.debug("Bound profile [{}] to address {{}}", name, NetworkAddress.format(boundSocket.get()));
         }
@@ -553,6 +553,7 @@ protected final void doClose() {
     protected final void doStop() {
         final CountDownLatch latch = new CountDownLatch(1);
         // make sure we run it on another thread than a possible IO handler thread
+        assert threadPool.generic().isShutdown() == false : "Must stop transport before terminating underlying threadpool";
         threadPool.generic().execute(() -> {
             closeLock.writeLock().lock();
             try {