Ahem.  Never mind.  When I recompiled the if_we.c driver to actually
print what kind of receive error it got, I found that it was CRC/frame
alignment errors.  Presumably my temporary lashup here is violating
the Ethernet specs somehow and I am being punished for it.  (I *think*
I should be well under the length limits, but perhaps not...)  Time to
get out the carpentry tools and do the network layout *right*.

As an aside, it shouldn't really be necessary to make code modifications
to tell the difference between "missed packet" errors and "CRC" errors...