Adjust argument sequences to C2x recommendations

While I don't see the whole picture there yet, it appears from this article that C2x will prefer a foo(size_t buffer_len, uint8_t *buffer) sequence of arguments (possibly to say foo(size_t buffer_len, uint8_t *buffer[buffer_len]) later, but dunno…).

Rearranging the arguments of all functions to be aligned with that is certainly not a bad idea as long as the API is still in flux.

@marcovr, can you tell me when it would be a good time for that from your branches' point of view?