INT 2A - NETWORK (Microsoft,LANtastic) - CHECK DIRECT I/O
        AX = 0300h
        DS:SI -> ASCIZ device name (may be full path or only drive specifier--
                must include the colon)
Return: CF clear if direct physical addressing (INT 13,INT 25) permissible
        CF set if access via files only
Notes:  do not use direct disk accesses if this function returns CF set or the
          device is redirected (INT 21/AX=5F02h)
        may take some time to execute
        called by DOS kernel on INT 25 and INT 26
SeeAlso: INT 25,INT 26,INT 21/AX=5F02h