virDomainActualNetDefContentsFormat: Format class_id only for status XML

In one of my previous patches (b68a56bc) I made class_id to
format more frequently. Well, now it's formatting way too
frequent - even for regular active XML. Users don't need to see
it, so lets format it only for the status XML where it's really
needed.
Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>

src/conf/domain_conf.c

@@ -18522,7 +18522,8 @@ virDomainActualNetDefContentsFormat(virBufferPtr buf,
 
         virBufferAddLit(buf, "/>\n");
     }
-    if (def->data.network.actual && def->data.network.actual->class_id) {
+    if (flags & VIR_DOMAIN_DEF_FORMAT_STATUS &&
+        def->data.network.actual && def->data.network.actual->class_id) {
         virBufferAsprintf(buf, "<class id='%u'/>\n",
                           def->data.network.actual->class_id);
     }