zap_cursor_serialize
*walk = zap_cursor_serialize(&zc);
*offp = zap_cursor_serialize(&cursor);
*offp = zap_cursor_serialize(&cursor);
uint64_t zap_cursor_serialize(zap_cursor_t *zc);
cursor = zap_cursor_serialize(&zc);
*cookiep = zap_cursor_serialize(&zc);
offset = zap_cursor_serialize(&zc);