`ipset list --name` is a privileged operation, and it prints an
"Operation not permitted" error when done as a normal user.
What's worse, this did it on loading (the command substitution wasn't
quoted), so we'd print the error as soon as you did `ipset `.
Only do the operation when necessary, and don't print the error.
This'll effectively only make it work for root shells (not e.g. `sudo
ipset`), but I don't want to sprinkle `sudo` in the completion.
(Also why does listing stuff require root? That's not how it works
e.g. for ips. But I don't actually know what ipset is for, so maybe
there is a good reason.)
[ci skip]
