the need to specify the unit number of unwired devices. ie: instead
of saying "device fxp0" we can say "device fxp" which is much closer
to what it actually means. The former (fxp0) implied something about
reserving the 0th unit, but it does not and never did - it was a
figment of config(8)'s imagination that we had to work around..
"device fxp0" simply means "compile in the fxp device driver", so we
may as well just write it as "device fxp" which is closer to what it
really means.
Doing this also saves us from filling up the ioconf.c tables with
meaningless entries.
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