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

[Ryan Stone]

Currently, if you remove an IPv4 address from an interface, all ARP
cache entries on its subnet are invalidated.  However, the same thing
is not done for NDP cache entries when an IPv6 address is removed*.
Is this correct behaviour?  It seems weird to have IPv4 and IPv6
behave differently.


* In a way this is a good thing as in6_lltable_prefix_free() is
guaranteed to crash your kernel in two different ways, and that's not
counting the race conditions that it's subject to.  I plan on
addressing these problems along with kern/165863, but in working on
that I realized that it was impossible to test any changes.