core: use NMActiveConnection objects throughout activation paths

They are the basic class that tracks active connections, and we're
going to use them for connection dependencies.  So use the fact that
both NMVPNConnection and NMActRequest have the same base class
instead of using object paths.

src/nm-activation-request.c

@@ -351,13 +351,35 @@ device_state_changed (NMDevice *device,
 
 /********************************************************************/
 
+/**
+ * nm_act_request_new:
+ *
+ * @connection: the connection to activate @device with
+ * @specific_object: the object path of the specific object (ie, WiFi access point,
+ *    etc) that will be used to activate @connection and @device
+ * @user_requested: pass %TRUE if the activation was requested via D-Bus,
+ *    otherwise %FALSE if requested internally by NM (ie, autoconnect)
+ * @user_uid: if @user_requested is %TRUE, the Unix UID of the user that requested
+ *    the activation
+ * @assumed: pass %TRUE if the activation should "assume" (ie, taking over) an
+ *    existing connection made before this instance of NM started
+ * @device: the device/interface to configure according to @connection
+ * @master: if the activation depends on another device (ie, VLAN slave, bond
+ *    slave, etc) pass the #NMActiveConnection that this activation request
+ *    should wait for before proceeding
+ *
+ * Begins activation of @device using the given @connection and other details.
+ *
+ * Returns: the new activation request on success, %NULL on error.
+ */
 NMActRequest *
 nm_act_request_new (NMConnection *connection,
                     const char *specific_object,
                     gboolean user_requested,
                     gulong user_uid,
                     gboolean assumed,
-                    gpointer *device)
+                    gpointer *device,
+                    NMActiveConnection *master)
 {
 	GObject *object;
 	NMActRequestPrivate *priv;