[PATCH] e100: correct rx_dropped and add rx_missed_errors

Do not count non-error frames dropped by the hardware as
part of rx_dropped. Instead, count those frames dropped as
rx_missed_errors. Also, do not count other error frames as part of
rx_dropped. Finally, do not count oversized frames in rx_dropped
(since they are counted as part of rx_length_errors).

Signed-off-by: John W. Linville <linville@tuxdriver.com>
Signed-off-by: Jeff Garzik <jgarzik@pobox.com>