btf_ext_visit_str_offs
r = btf_ext_visit_str_offs(d->btf_ext, fn, ctx);
int btf_ext_visit_str_offs(struct btf_ext *btf_ext, str_off_visit_fn visit, void *ctx);
err = err ?: btf_ext_visit_str_offs(obj->btf_ext, check_btf_str_off, obj->btf);