IB/iser: bound protection_sg size by data_sg size

IB/iser: bound protection_sg size by data_sg size

In case we don't set the sg_prot_tablesize, the scsi layer assign the
default size (65535 entries). We should limit this size since we should
take into consideration the underlaying device capability. This cap is
considered when calculating the sg_tablesize. Otherwise, for example,
we can get that /sys/block/sdb/queue/max_segments is 128 and
/sys/block/sdb/queue/max_integrity_segments is 65535.

Link: https://lore.kernel.org/r/1569359027-10987-1-git-send-email-maxg@mellanox.com
Signed-off-by: Max Gurtovoy <maxg@mellanox.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>