bitfields are a pain to use when dealing with structures with a fixed
layout in memory (you have to worry about bit order, for example).
Don't assume that the Ethernet header is aligned on a 2-byte boundary -
use "pntohs()" to extract stuff from it. (Perhaps C will force it onto
a 2-byte boundary, but why take chances, and why leave the code
vulnerable to changes outside this module?)
Don't assume that the pointers to the IP and TCP headers are nicely
aligned - use "memcpy()", not structure assignment, to copy the headers.
(They're probably *not* nicely aligned on platforms that require 4-byte
alignment of 4-byte integral quantities; the code was dumping core on
SPARC with an alignment error.)
Don't even make those pointers be pointers to structures, as that may
cause the C compiler to generate in-line 4-byte loads and stores for
"memcpy()" (in fact, it *did* do so with GCC 2.95.1 on SPARC), which has
the same problem as structure assignment.
Don't test the IP protocol number twice when handling PPP.
svn path=/trunk/; revision=4378
