[CIFS] Fix mapping of old SMB return code Invalid Net Name so it is

recognized on mount

the old mapping of this was to ENODEV (instead of ENXIO) - but
ENODEV is what mount returns when the cifs driver will not load
so change this to map to ENXIO (which was what the equivalent
condition returned for mapping errors from more modern servers)

Signed-off-by: Steve French <sfrench@us.ibm.com>