Heads-up: ifconfig address without a mask/width to become an error

It is currently possible to specify an IPv4 address without a
netmask/width to ifconfig or in rc.conf, e.g.:

    ifconfig_igb0="192.168.0.2"

phk recently discovered[1] that ifconfig chose a poor netmask/width
when none was specified. This was not an intentional change in
defaults but rather a bug that has now been fixed by grembo@, in
commit 8a9f0fa42b1c and merged to stable/14 in 048ad7a9ef9f. The fix
will be in FreeBSD 14.2. I am unsure if there will be an EN update for
14.0/14.1. The bug does not exist in FreeBSD 13.x.

Specifying an IPv4 address without a mask/width has been deprecated
since the deprecation of classful addressing. As of FreeBSD 13.1
ifconfig has emitted a warning when no mask/width is specified, and
the intent was to make it an error after a sufficient amount of time
passed.

I've opened a Phabricator review[2] for ifconfig to change the warning
into an error. I included a link to the review in phk's thread, and
asked for input on timing for landing the change. As there seems to be
consensus to include this change in FreeBSD 15.0 I plan to commit it
soon and am sending this note to increase the visibility of the
upcoming change.

This will be prominently noted in the 15.0 release notes, and should
be mentioned in release notes for upcoming 13.x and 14.x releases.

[1] https://lists.freebsd.org/archives/freebsd-current/2024-June/006047.html
[2] https://reviews.freebsd.org/D45585