[e2e] UDP length field

[minshall at redback.com (Greg Minshall)]

Joe,

> 	3. in the case where IP options add trailers
> 		in this case, there is insufficient information in the IP_LEN
> 		and IP_HLEN fields to determine where the UDP data ends

foo.  if an IP option adds a trailer, it needs to give an indication of how to 
find that trailer, which is in "IP land", not "UDP/TCP/whatever land" (note 
that in rfc893, "how to find the trailer" is actually in "ethernet land"; that 
works, since rfc893 is effectively describing an ethernet option that adds a 
trailer).

cheers, Greg Minshall