MXS-2196: Pass Listener into dcb_accept

Modified the functions to use a listener instead of a DCB in the accepting
process. This removes some of the dependenices that the listeners have on
the DCB system.

server/modules/protocol/HTTPD/httpd.cc

@@ -363,7 +363,7 @@ static int httpd_accept(DCB* listener)
     int n_connect = 0;
     DCB* client_dcb;
 
-    while ((client_dcb = dcb_accept(listener)) != NULL)
+    while ((client_dcb = dcb_accept(listener->listener)) != NULL)
     {
         HTTPD_session* client_data = NULL;