IB/iser: Generalize map/unmap dma tasks

Avoid code duplication and add the mapping/unmapping of the protection
buffers to the iser_dma_map_task_data/iser_dma_unmap_task_data functions.

Link: https://lore.kernel.org/r/20220308145546.8372-4-mgurtovoy@nvidia.com


Reviewed-by: Sergey Gorenko <sergeygo@nvidia.com>
Signed-off-by: Max Gurtovoy <mgurtovoy@nvidia.com>
Acked-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>