INT 2F U - DOS 3+ internal - OPEN DEVICE AND SET SFT OWNER???
        AX = 120Ch
        SDA current SFT pointer -> SFT for file
        DS = DOS DS
        SS = DOS DS (must be using a DOS internal stack)
Return: ES, DI, AX destroyed
Notes:  invokes "device open" call on device driver for SFT
        changes owner of last-accessed SFT to calling process if it was opened
          via FCB
        called by network redirectors such as MSCDEX