* Add a slot in the softc, ep_pktlenshift, to indicate that
a board implements ``large packets'' (FDDI-sized frames) and
therefore implicitly shifts the argument to packet-length commands
by two bits to fit a 13-bit length in an 11-bit command argument field.
* Change the reset of station-mask filterto be independent of bus-type
(e.g.,. for 3c515)
* Replace the "2044" constant used to disable TX threshold interrupts
on 3c509-generation cards with a #define. Use 2047 instead,
since that works on the large-packet cards (Vortex, Demon, Boomerang)
and 2044 doesn't.
* Add code to epconfing to probe for large-packet support,
set the softc appropriately, and shift packet sizes in commands
by ep_pktlenshift to compensate for the implicit shift.
* Tweak the epconfig() code to avoid hanging on startup.
Set the Tx threshold to interrupt when there's space for
a maximal-sized ether frame, then do epinit() then epstop(),
instead of just the Tx and Rx reset. Required on at least a 3c595.
Tested on a 3c595, but not on 3c509-generation hardware.
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