portal network monitor: Do autostart

There is no explicit starting of the portals in the
session, so best to allow autostart here. There has
been at least one epiphany bug reported that can be
described as "epiphany thinks I'm offline and there's
a warning about a D-Bus name without an owner and a
proxy without autostart."
diff --git a/gio/gnetworkmonitorportal.c b/gio/gnetworkmonitorportal.c
index 9a5820a..2c0eb8a 100644
--- a/gio/gnetworkmonitorportal.c
+++ b/gio/gnetworkmonitorportal.c
@@ -432,8 +432,7 @@
     }
 
   proxy = g_dbus_proxy_new_for_bus_sync (G_BUS_TYPE_SESSION,
-                                         G_DBUS_PROXY_FLAGS_DO_NOT_AUTO_START
-                                         | G_DBUS_PROXY_FLAGS_DO_NOT_LOAD_PROPERTIES,
+                                         G_DBUS_PROXY_FLAGS_DO_NOT_LOAD_PROPERTIES,
                                          NULL,
                                          "org.freedesktop.portal.Desktop",
                                          "/org/freedesktop/portal/desktop",