pmtud + ipnat RELENG_6_2 appears to be broken

[Pete French]

> lagg on RELENG_6 is currently broken due to subtle differences that
> wernt taken into account when it was MFCd. Can you please test this
> patch.

Erp! Do you have any mor einfo on tyhis - what kinds of things does
this break ? Since lagg arrived I have deployed it on all our production
machines. It seems to work fine for me, I have to say, but I would like to
know what problems I might be about to encounter.

Will apply and test your patch (though having seen no problems anyway I
am not sure how useful that will be).

-pcf.