Workaround for mpd5 and 8.0 broken proxy arp?

[Li, Qing]

Hi Ruslan,

> 
> Doesn't seem to have any effect.  Please see
> http://lists.freebsd.org/pipermail/freebsd-net/2010-March/024728.html
> on how to reproduce.
> 

Could you please try the patch at:

	http://people.freebsd.org/~qingli/ng-patch.diff

I was able to reproduce the problem and the patch appears to fix
this if_ng issue now.

I also tested a couple of other reported cases and those continue
to function.

Please give this new patch a try and let me know how it works out.

Thank you.

-- Qing