Fix AttachmentMtomChunkingTest port collision with AttachmentChunkingTest

Both tests have an inner class named DownloadServer and use
allocatePort(DownloadServer.class). Since TestUtil stores ports under
the simple class name, both tests get the same port, causing
ListenerRegistrationException when the second test tries to publish
its endpoint.

Fix by using allocatePort(AttachmentMtomChunkingTest.class) to get a
distinct port.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: gnodet

systests/jaxws/src/test/java/org/apache/cxf/systest/jaxws/AttachmentMtomChunkingTest.java

@@ -44,7 +44,7 @@
 import static org.junit.Assert.assertTrue;
 
 public class AttachmentMtomChunkingTest extends AbstractAttachmentChunkingTest {
-    private static final String PORT = allocatePort(DownloadServer.class);
+    private static final String PORT = allocatePort(AttachmentMtomChunkingTest.class);
     private static final Logger LOG = LogUtils.getLogger(AttachmentMtomChunkingTest.class);
 
     public static class DownloadServer extends AbstractBusTestServerBase {