Expose groups by default in ifconfig output. This was never hidden by
OpenBSD; unsure why we chose to do so. As groups are a requirement for
pf, exposing them by default will make our pf implementation less
confusing.

While here add a missing free() that OpenBSD fixed 7 years ago.

PR: 194925
Differential Revision: https://reviews.freebsd.org/D1185
Approved by: des
Obtained from: OpenBSD