scsi: IB/iser: set virt_boundary_mask in the scsi host

This ensures all proper DMA layer handling is taken care of by the SCSI
midlayer.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by: Max Gurtovoy <maxg@mellanox.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>