IPv6: Report another invalid case as invalid, not truncated

IPv6: Report another invalid case as invalid, not truncated

This is in the jumbo case.

When the payload+header length is > (original) length, output example:
  [payload+header length 65577 > length 65576] (invalid)

We treat this as a warning and so don't stop decoding (as before).

Add a test file.

Update two test outputs accordingly.