Fix WRITE SAME data buffer length handling

From the SPC-4 paragraph about WRITE SAME(10): "The WRITE SAME (10)
command requests that the device server transfer a single logical
block from the Data-Out Buffer [ ... ]". Hence always pass a data
buffer when sending a WRITE SAME(10) command.

Set the NDOB bit in the WRITE SAME(16) command if no data out buffer
is present.

Signed-off-by: Bart Van Assche <bvanassche@acm.org>

test-tool/test_writesame10_unmap_until_end.c

@@ -54,8 +54,8 @@ test_writesame10_unmap_until_end(void)
 
 		logging(LOG_VERBOSE, "Unmap %d blocks using WRITESAME10", i);
 		ret = writesame10(iscsic, tgt_lun, num_blocks - i,
-				  0, i,
-				  0, 1, 0, 0, NULL);
+				  block_size, i,
+				  0, 1, 0, 0, buf);
 		CU_ASSERT_EQUAL(ret, 0);
 
 		if (rc16->lbprz) {