RE: [DNA] Revised terminology section for DNAv4

[Alper Yegin <alper.yegin@samsung.com>]

> Link Down
>      An event provided by the link layer that signifies a state change
>      associated with the interface no longer being capable of
>      communicating IP packets.
> Link Up
>      An event provided by the link layer that signifies a state change
>      associated with the interface becoming capable of communicating
IP
>      packets.

I think the main document to define these terms is the "L2 event
notifications for DNA" (dna-link-info) I-D. We could have the DNAv4 and
DNAv6 solution drafts point to it. But since DNAv4 I-D is ahead in the
process, we'd have to include them in that document as well. I'd
recommend adding a reference to dna-link-info for a more detailed
discussions on the link up/down.

Alper