metadata: filter for the "default" metadata object in all places where we use it

there can be more metadata objects around...

src/scripts/policy-endpoint-client-links.lua

@@ -202,7 +202,12 @@ if mixer_api then
   endpoints_om:activate()
 end
 
-metadatas_om = ObjectManager { Interest { type = "metadata" } }
+metadatas_om = ObjectManager {
+  Interest {
+    type = "metadata",
+    Constraint { "metadata.name", "=", "default" },
+  }
+}
 metadatas_om:connect("object-added", function (om, metadata)
   metadata:connect("changed", function (m, subject, key, t, value)
     if key == "suspend.playback" then

src/scripts/policy-node.lua

@@ -284,7 +284,12 @@ function reevaluateSiLinkables ()
 end
 
 default_nodes = Plugin.find("default-nodes-api")
-metadatas_om = ObjectManager { Interest { type = "metadata" } }
+metadatas_om = ObjectManager {
+  Interest {
+    type = "metadata",
+    Constraint { "metadata.name", "=", "default" },
+  }
+}
 siendpoints_om = ObjectManager { Interest { type = "SiEndpoint" }}
 silinkables_om = ObjectManager { Interest { type = "SiLinkable",
   -- only handle si-audio-adapter and si-node

src/tools/wpctl.c

@@ -577,7 +577,10 @@ set_default_parse_positional (gint argc, gchar ** argv, GError **error)
 static gboolean
 set_default_prepare (WpCtl * self, GError ** error)
 {
-  wp_object_manager_add_interest (self->om, WP_TYPE_METADATA, NULL);
+  wp_object_manager_add_interest (self->om, WP_TYPE_METADATA,
+      WP_CONSTRAINT_TYPE_PW_GLOBAL_PROPERTY,
+      "metadata.name", "=s", "default",
+      NULL);
   wp_object_manager_add_interest (self->om, WP_TYPE_NODE,
       WP_CONSTRAINT_TYPE_PW_GLOBAL_PROPERTY,
       "object.id", "=u", cmdline.set_default.id,