[e2e] UDP length field

[Craig Partridge]

Quick addendum regarding the UDP length mismatch.

If there's no UDP checksum and the two lengths don't agree but UDP len < IP len
we can either accept or reject.  I actually don't have a strong view as to
which result is correct.  Given that my prior note said UDP len < IP len
is an acceptable condition, the "liberal in what you accept from others"
principle presumably says take the datagram.  On the other hand, there's
no good reason, short of pilot error, for the two lengths to disagree,
which suggests rejection.

Craig