net/mtr broken without ipv6

[Lena at lena.kiev.ua]

> I build my custom kernel without IPv6 since I'm not going to be using
> it any time soon. The mtr port doesn't work anymore

> What can I do to fix this without enabling a useless (to me) option in my
> kernel and rebuilding?

Downgrade the mtr port to mtr-nox11-0.82_1.
I update ports tree with `portsnap` and use `svn export`
(devel/subversion port) for downgrading a single port.
How to learn the revision for downgrading:

svn log svn://svn0.us-east.freebsd.org/ports/head/net/mtr | less

How to downgrade:

rm -rf /usr/ports/net/mtr
svn export -r r300897 svn://svn0.us-east.freebsd.org/ports/head/net/mtr /usr/ports/net/mtr
portupgrade -f mtr\*