Fix advertised JNLP Port

As far as I can figure, the /TcpSlaveAgentListener/ endpoint headers
tell the slaves what the JNLP port is. When I'm running jenkins behind a
proxy (marathon using the mesos plugin, which bridged networking), even
though I was setting the advertised port per a thread[1], it was not
accurately being returned in the header. This patch fixes that.

[1] https://groups.google.com/d/topic/jenkins-mesos/qUrXpDY07TQ/discussion

core/src/main/java/hudson/Functions.java

@@ -1925,7 +1925,7 @@ public class Functions {
 
             TcpSlaveAgentListener tal = j.tcpSlaveAgentListener;
             if (tal !=null) {
-                int p = TcpSlaveAgentListener.CLI_PORT !=null ? TcpSlaveAgentListener.CLI_PORT : tal.getPort();
+                int p = tal.getAdvertisedPort();
                 rsp.setIntHeader("X-Hudson-CLI-Port", p);
                 rsp.setIntHeader("X-Jenkins-CLI-Port", p);
                 rsp.setIntHeader("X-Jenkins-CLI2-Port", p);