ibmvscsis: Add SGL limit

This patch adds internal LIO sgl limit since the driver already
sets a max transfer limit on transport layer of 1MB to the client.

Cc: stable@vger.kernel.org
Tested-by: Steven Royer <seroyer@linux.vnet.ibm.com>
Signed-off-by: Bryant G. Ly <bryantly@linux.vnet.ibm.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>