DEX: Flow-ID and Sequence Number detection

[talmi]

The current draft specifies:
The length of
the DEX option is either 8 octets or 16 octets, as the Flow ID and
the Sequence Number fields (summing up to 8 octets) are optional. It
is assumed that the lower layer protocol indicates the length of the
DEX option, thus indicating whether the two optional fields are
present.

It was noted that this approach is not recommended as it does not allow to add new fields in the future.

[shwethab]

Per design team meeting on 6th May 2020: there is agreement on using separate flags to indicate presence of optional flags.