Entry in Roe Mapper table. It creates or edits a mapper of structure-agnostic type when the encap-mode of the corresponding roe is structure-agnostic. In structure-agnostic mode, at most 1 mapper can be created in a roe entity. When a mapper is created, the create keyword must be specified. By default, no mappers exist until they are explicitly created. The mapper can be deleted only after it is shutdown.