em0 performance subpar

[Jack Vogel]

Adam,

The TX ring for the legacy driver is small right now compared to em, try
this experiment,
edit if_lem.c, search for "lem_txd" and change EM_DEFAULT_TXD to 1024, see
what
that does, then 2048.

My real strategy with the legacy code was that it should stable, meaning not
getting
a lot of changes... that really hasn't worked out over time. I suppose I'll
have to try and
give it some tweaks and let you try it. The problem with this code is it
technically supports
a huge range of old stuff we don't test any more, things I do might cause
other regressions :(

Oh well, let me know if increasing the TX descriptors helps.

Jack