Split the tunnel-p2p-params_config grouping in multiple groups

[italobusi]

Pull request to propose a fix to open issue #31

Three groupings have been created, while waiting them to be re-defined in te-types

[italobusi]

I think it would be simpler to split the grouping into multiple groupings rather than just two

It seems that the ignore-overload has been removed from the latest version of the TE Tunnel model

I am still not sure we need the preference attribute from the resolution of https://github.com/ietf-mpls-yang/te/issues/16

@efralaz : could you please confirm whether we need the preference attribute as an input for the Path Computation RPC?

If we are ok with this proposal, I can propose the required changes to the te-types and te models

[italobusi]

Carlo/Francesco/Italo/Sergio:

The preference attribute would be needed to request multiple attempts for path computation, as under discussion with TE Tunnel authors in https://github.com/ietf-mpls-yang/te/issues/18

We can propose the preference grouping definitions to be added to the te-types model and remove it from the current path-computation model

We can evaluate whether to use it or not when resolving open issue #35

[italobusi]

Pending merge of pull request https://github.com/ietf-mpls-yang/te/pull/27

[italobusi]

Thinking further, this pull request provides a work-around that could be used while waiting for the TE tunnel updates

I would propose to merge this pull request before requesting YANG doctor review and to re-open issue #31 to track the need to update the YANG model after the merging of pull request ietf-mpls-yang/te#27

[italobusi]

Superceeded by pull request #50