The Type of Service or Differentiated Services Code Point
value and mask to be associated with this Class of Service.
If this field is returned as <empty-string>, then it has not
been configured and no action will be taken for this
attribute. The first octet shall represent the TOS/DSCP value
and the second octet shall represent the mask applied to that
value. Agents that do not support masking shall fail sets to
this object that include a mask octet.