Hi,
The card does not support 100 modules/cables.
I double-checked and the LST7G48SX6E0 board only supports this following module:
Please see in the https://support.huawei.com/hedex/hdx.do?docid=EDOC1100126511&id=EN-US_CONCEPT_0177096828&lang=en
The 100Base-FX is not included. That is why you cannot set the speed.
Glad to help you! Any further questions, let us know.