IB/iser: Support up to 16MB data transfer in a single command

IB/iser: Support up to 16MB data transfer in a single command

Maximum supported IO size is 8MB for the iSER driver. The current value is
limited by the ISCSI_ISER_MAX_SG_TABLESIZE macro. But the driver is able
to handle 16MB IOs without any significant changes. Increasing this limit
can be useful for the storage arrays which are fine tuned for IOs larger
than 8 MB.

This commit allows to configure maximum IO size up to 16MB using the
max_sectors module parameter.

Link: https://lore.kernel.org/r/20190912103534.18210-1-sergeygo@mellanox.com
Signed-off-by: Sergey Gorenko <sergeygo@mellanox.com>
Reviewed-by: Max Gurtovoy <maxg@mellanox.com>
Acked-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>