vl: Document why objects are delayed

Objects should not be "delayed" without a reason, as the previous
commit demonstrates.  The remaining ones have reasons.  State them.
and demand future ones come with such a statement.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20190604151251.9903-3-armbru@redhat.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

vl.c

@@ -2751,19 +2751,25 @@ static bool object_create_initial(const char *type, QemuOpts *opts)
         exit(0);
     }
 
+    /*
+     * Objects should not be made "delayed" without a reason.  If you
+     * add one, state the reason in a comment!
+     */
+
+    /* Reason: rng-egd property "chardev" */
     if (g_str_equal(type, "rng-egd")) {
         return false;
     }
 
 #if defined(CONFIG_VHOST_USER) && defined(CONFIG_LINUX)
+    /* Reason: cryptodev-vhost-user property "chardev" */
     if (g_str_equal(type, "cryptodev-vhost-user")) {
         return false;
     }
 #endif
 
     /*
-     * return false for concrete netfilters since
-     * they depend on netdevs already existing
+     * Reason: filter-* property "netdev" etc.
      */
     if (g_str_equal(type, "filter-buffer") ||
         g_str_equal(type, "filter-dump") ||