objnamedtuple: Support iteration.

py/objnamedtuple.c

@@ -160,6 +160,7 @@ mp_obj_t mp_obj_new_namedtuple_type(qstr name, const char *fields) {
     o->base.load_attr = namedtuple_load_attr;
     o->base.store_attr = namedtuple_store_attr;
     o->base.subscr = tuple_subscr;
+    o->base.getiter = tuple_getiter;
     o->base.bases_tuple = (mp_obj_t)&namedtuple_base_tuple;
     o->fields = fields;
     return o;