Hm, I'm not sure why this information should require root access. I
can do --iflist as an unprivileged user on my Linux box. Can you try
as an unprivileged user with Nmap 4.23RC2 and (if 4.23RC2 also shows
the error) 4.20 on the same OS X box and see what happens? That will
tell us whether this is a new error or has long existed.