NFS Auth per-zone needs better cleanup

@@ -278,10 +278,13 @@
 
         list_destroy(&nag->refreshq_queue);
         cv_destroy(&nag->refreshq_cv);
         mutex_destroy(&nag->refreshq_lock);
         mutex_destroy(&nag->mountd_lock);
+        /* Extra cleanup. */
+        if (nag->mountd_dh != NULL)
+                door_ki_rele(nag->mountd_dh);
         kmem_free(nag, sizeof (*nag));
 }
 
 /*
  * Convert the address in a netbuf to