IB/iser: Publish T10-PI support to SCSI midlayer

After allocating a scsi_host we set protection types and guard type
supported.

Signed-off-by: Sagi Grimberg <sagig@mellanox.com>
Signed-off-by: Alex Tabachnik <alext@mellanox.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>