This is the maximum possible size of this page.
Previouslly we only read the arbitrary 255 bytes of page, but for targets
that return >255 bytes of data this would then incorrectly make the test fail
since the data-in buffer was truncated and thus the inq->additional_length
no longer matched up with the datain buffer size.
Now reading up to 260 bytes will avoid the datain buffer from ever becomming truncated, and as a second feature also make sure to test that the target
understands > 8-bit values for the allocation length in the request.
