Replace kMaxIetfVarInt with UINT32_MAX, as size_t on 32-bit platforms is smaller than kMaxIetfVarInt, thus causing a compile error on those platforms. gfe-relnote: n/a (test-only change) PiperOrigin-RevId: 278843731 Change-Id: I0f8174404e8b524a10afe856a7b8e612d720e3d9