TLR is necessary for reliable communication with SAS tape drives.
This was broken by change 246713 in the mps(4) driver. It changed the
cm_data field for SCSI I/O requests to point to the CCB instead of the data
buffer. So, instead, look at the CCB's data pointer to determine whether
or not we're talking to a tape drive.
Also, take the residual into account to make sure that we don't go off the
end of the request.
MFC after: 3 days
Sponsored by: Spectra Logic Corporation
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