Return the DOFInterfaceMethod that is associated with the Invoke Operation. 
- Lifecycle
 - The data returned is owned by the DOFOperation and is only valid as long as the DOFOperation remains valid. It must not be destroyed individually.
 
- Parameters
 - 
  
    | op | The Operation. This must not be NULL and must represent a valid Invoke Operation. | 
  
   
- Returns
 - The associated DOFInterfaceMethod. This will not be NULL.