Why does V2GTP20_ReadHeader expect me to know the payload ID?

Hi there,

I have a quick question behind the intention of

`int V2GTP20_ReadHeader(const uint8_t* stream_data, uint32_t* stream_payload_length, uint16_t v2gtp20_payload_id);`

Why does this signature expect the caller to know the payload id? When receiving data, you have no clue what type of payload you will receive. Probing until `V2GTP20_ReadHeader` returns without error seems a little cumbersome, doesn't it?

Cheers,
Richard