The file system device for which files will be displayed in the
FileViewer table. The values supported for this variable are
identical to the values for other variables in the MIB, although not
all values will actually result in the display of files.
The different devices and whether they will result in the display
of files are:
1. Flash - Onboard Flash - supported
2. Card - Removable SD card - supported
3. NVS - Onboard battery backed RAM - supported
4. TFTP - not supported
5. USB - Removable USB media - supported
Setting this variable to an unsupported value will result in an error,
but setting to a value that is supported but on a device that doesn't
contain that type of device will not. However, no files will be
displayed in the File Viewer table in this case.