IB/iser: Protect iscsi_max_lun module param using callback

Remove the check from the module_init function.

Link: https://lore.kernel.org/r/20210111145754.56727-3-mgurtovoy@nvidia.com


Reviewed-by: Israel Rukshin <israelr@nvidia.com>
Signed-off-by: Max Gurtovoy <mgurtovoy@nvidia.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>