[manet] packetbb update idea

[Justin Dean <[e-mail]>]

So while trying to encode some information using packetbb for the elastic
multicast stuff we have been working on I've run into a short coming.
RFC5444 allows one to efficiently encode information about addresses and
even pairs of addresses (as long as one of those addresses is the Oaddr)
with the TLV structure and the address block.  It does not allow for easy
encoding about pairs of addresses of which neither is the Oaddr.  After
some thinking on it I think most of what I'd like to be able to do could be
solved by using the RESERVED tlv flag bit number 6 to indicate inclusion of
a single index field <index-opt> which would specify a single address in
the address block.
So the tlv definition would change from
<tlv> := <tlv-type>

                <tlv-flags>
                <tlv-type-ext>?
                (<index-start><index-stop>?)?
                (<length><value>?)?

to

<tlv> := <tlv-type>
                <tlv-flags>
                <tlv-type-ext>?

                <index-opt>?
                (<index-start><index-stop>?)?
                (<length><value>?)?


This would allow one to specify information about pairs of addresses in a
compact way.  In the case of elastic multicast source/destination flow
pairs. Thoughts welcome.

Justin