libsmi error group-membership

Error text: node `__' must be contained in at least one conformance group

Reference: RFC 2580 section 3.1

   It is required that every object defined in an information module
   with a MAX-ACCESS clause other than "not-accessible" be contained in
   at least one object group.  This avoids the common error of adding a
   new object to an information module and forgetting to add the new
   object to a group.