If the read or write request can fit into a 6-byte cdb, then
use a 6-byte cdb, otherwise use the 10-byte as before.
In sd.c:
In sdattach(), make a note if the device is "ancient" (i.e.
inqbuf.version & SID_ANSII == 0).
Implement sdminphys(): if the device is "ancient", shorten the
transfer so it will fit into a 6-byte cdb.
These changes have eliminated the rejected read/write requests on my
Sun 3/60 with 2 ESDI disks behind an Emulex MD21.
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