[mpls] mpls-open-dt: ancillary data commens

[Toerless Eckert <[e-mail]>]

a) Suggest to replace:
   Types of ancillary data
   with
   Positioning of ancillary data

   Types is an overloaded term and make me for example foremost think it means semantics.
   Positioning should hopefully be more precisely describin what this point describes.

b) Wrt the discuss on control plane learned ancillary data,

   i suggest to add the following a new section:

---
Source of semantics 

   The semantic of or associated with ancillary data can come from different sources 
   depending on scope of the ancillary data semantic:
   - network wide
     - by standard
     - through network-wide control plane 
   - per-class
     - through control plane
   - per-flow
     - through per-flow control plane

   Consistency for network-wide control plane was raised as core new issue,
   unclar if e.g.: IGP eventual consistency is suficient here.

   For per-class control plane (e.g. DSCP/EXP static config) and per-flow control plane 
   (e.g. RSVP-TE signaling) we have accepted models.
---

Cheers
    Toerless