Removing an IPv6 address does not remove NDP entries on that subnet

[Li, Qing]

>
> [rstone at vm-head ~]ndp -a
> Neighbor                             Linklayer Address  Netif Expire    S Flags
> 1::2                                 08:00:27:1e:b8:16    em0 7s        R
> fe80::a00:27ff:fefa:8732%em0         08:00:27:fa:87:32    em0 permanent R
> rstone at vm-head ~]uname -a
> FreeBSD vm-head 10.0-CURRENT FreeBSD 10.0-CURRENT #10 r233549:233552M:
> Wed Mar 28 10:27:20 EDT 2012
>

I don't know when this basic functionality was broken. I cannot verify when the breakage
occurred on the 8.x systems I have because I am traveling at the moment.

I can take ownership of this bug and get it fixed as soon as I return in 1.5 weeks.

--Qing