TESTS: Test that WRITESAME10/16 unmap can handle big number of logical blocks when unmapping.

If  BLockLimits->MaxWriteSameLength is 0 (no limit) or >=256
then verify that both WRITESAME10 and WRITESAME16 can unmap with a
number of blocks == 2 byte field.
If not, then verify that a 256 block unmap results in INVALID FIELD IN CDB

If  BLockLimits->MaxWriteSameLength is 0 (no limit) or >=65536
then verify that WRITESAME16 can unmap with a
number of blocks == 3 byte field.
If not, then verify that a 65536 block unmap results in INVALID FIELD IN CDB

From discussions on linux-scsi there are devices that support WRITESAME16
but where the implementation only looks at the low 2 bytes of the 4 bytes for
num-blocks in the CDB.
This added test aims to find and flag such devices.

test-tool/iscsi-support.c

@@ -48,6 +48,7 @@ const char *tgt_url;
 
 struct scsi_inquiry_standard *inq;
 struct scsi_inquiry_logical_block_provisioning *inq_lbp;
+struct scsi_inquiry_block_limits *inq_bl;
 struct scsi_readcapacity16 *rc16;
 
 size_t block_size;