Begins by writing a @start byte in the first position of @buffer and
then for every next byte it stores the value of its previous one
incremented by one.

Behaves the same for both supported flags.
Signed-off-by: NIlias Stamatis <stamatis.iliass@gmail.com>
Reviewed-by: NJán Tomko <jtomko@redhat.com>
Signed-off-by: NJán Tomko <jtomko@redhat.com>