dns: fix NMDnsPluginPrivate and drop unused fields

NM_DNS_PLUGIN_GET_PRIVATE() macro was broken. Also NMDnsPluginPrivate
contained unused fields. Fix that.

The private data is unused at the moment, but will be used next.
Hence it is fixed and not removed.

src/core/dns/nm-dns-plugin.c

@@ -18,10 +18,7 @@
 /*****************************************************************************/
 
 typedef struct _NMDnsPluginPrivate {
-    GPid  pid;
-    guint watch_id;
-    char *progname;
-    char *pidfile;
+    int _dummy;
 } NMDnsPluginPrivate;
 
 G_DEFINE_ABSTRACT_TYPE(NMDnsPlugin, nm_dns_plugin, G_TYPE_OBJECT)
@@ -110,9 +107,19 @@ nm_dns_plugin_stop(NMDnsPlugin *self)
 static void
 nm_dns_plugin_init(NMDnsPlugin *self)
 {
+    NMDnsPluginPrivate *priv;
+
+    priv = G_TYPE_INSTANCE_GET_PRIVATE(self, NM_TYPE_DNS_PLUGIN, NMDnsPluginPrivate);
+
+    self->_priv = priv;
+
     nm_shutdown_wait_obj_register_object(self, "dns-plugin");
 }
 
 static void
-nm_dns_plugin_class_init(NMDnsPluginClass *plugin_class)
-{}
+nm_dns_plugin_class_init(NMDnsPluginClass *klass)
+{
+    GObjectClass *object_class = G_OBJECT_CLASS(klass);
+
+    g_type_class_add_private(object_class, sizeof(NMDnsPluginPrivate));
+}

src/core/dns/nm-dns-plugin.h

@@ -19,8 +19,11 @@
 #define NM_DNS_PLUGIN_GET_CLASS(obj) \
     (G_TYPE_INSTANCE_GET_CLASS((obj), NM_TYPE_DNS_PLUGIN, NMDnsPluginClass))
 
+struct _NMDnsPluginPrivate;
+
 typedef struct {
     GObject                     parent;
+    struct _NMDnsPluginPrivate *_priv;
 } NMDnsPlugin;
 
 typedef struct {