Add text to PNA specification on encrypt/decrypt operations

[jfingerh]

While it is definitely valuable to have comments in the definition of the extern, it would also be useful to give some text in the body of the PNA specification, in its own section, describing the basic idea of this extern, when and how its methods should be called, and what their effect is.

@pbhide Is this something you would be willing to write? Or anyone you can suggest that you can persuade to volunteer for the task?

[pbhide]

Will work on it in 1st week of dec.

[pbhide]

@jfingerh any recommendation on the section in PNA spec where this should go?
I can think of adding it in section 6 (after 6.10 packet recirculation section, which seems empty btw). OR
I can add it in section 7.
I was looking for a section for "recommended/Required" externs in PNA spec but don't see one.
Are we going to specify certain extern functions/objects as - "PNA compliant target SHALL support the following extern methods and objects..."

[jafingerhut]

I would recommend a new sub-section of section 7, since it is an extern object we are explaining.

[jafingerhut]

So far there has been little use of MUST/SHALL/SHOULD capitalized like many IETF RFCs have in P4.org specifications. We can discuss whether there should be, but that is the current state of things.