hotfix for nr_rrc_data_req for the unfortunate SDU size 255
hotfix to avoid checking for sdu_sizeP=255 in nr_rrc_data_req. If ever the SDU has this size the function will return. This is an old piece of code where 255 meant -1 which was what was returned from the asn1c encoding function if the ASN.1 message was not encodable.