mask set is non-contiguous. We don't prohibit setting such things
(even if they are basically useless) so they can be set by accident.
ifconfig ifN 10.0.0.1 netmask 225.0.0.0
produced
ifN .. inet 10.0.0.1/8
with the previous form (since 225 is 0xE1), now it produces
ifN ... inet 10.0.0.1 netmask 0xe1000000
If the "netmask" form ever appears in ifconfig output, it (now)
means that the netmask is non-contig, which should make that case
obvious (whther intended, or set by accident)
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