BERT for non-reliable transports

[chrysn]

Closes: #17

This may need a bit of iteration (esp. w/rt the normative update text), but it's a starting point.

[cabo]

I like this initiative a lot, and the text looks good.
But is this something that can be done without an RFC, i.e., is corr-clar the right venue?
I'm almost thinking that we should have added this to groupcomm-bis, which we just pushed to the IESG.

[chrysn]

It will need an RFC that Updates 7959; can be a reason to eventually publish this, or to spin small documents from text once it is ready here. If nothing else, having this in a consensus section in a WG document already assurer users that szx=7 won't mean anything but BERT.

[chrysn]

I've added a commit that contains pointers discussed in today's interim, namely, how the relevant reassembly size for OSCORE could be communicated.