TimeSync: Deactivated attributes versus disabled attributes.

In general fashion, we can currently deactivate attributes by means of the flag CIP_FLG_TREAT_DISABLE. The user has the possibility to modify the attribute flags over the DPM, so he can activate that attribute at any time.

Sometimes, e.g., for attributes 16 and 17 of the iImeSync object, we do not implement an attribute at all and want it to be disabled once and forever during the whole system runtime. Therefore, different approaches can be made:

1) Rename attribute flag CIP_FLG_TREAT_DISABLE to CIP_FLG_TREAT_DEACTIVATE and introduce new CIP_FLG_TREAT_DISABLE which can not be modified. Most generic approach, but invasive. API change.

2) Forbid the modification of the attribute flags for disabled attributes. This could easily be achieved on a per-object basis. This is the preferred approach.

-> Forbid modification of the attribute options (i.e. attribute flags) of attributes 16 and 17 of the timesync object instance.