When tearing down vnet jails we can move an if_bridge out (as
part of the normal vnet_if_return()). This can, when it's clearing out
its list of member interfaces, change its link layer address.
That sends an iflladdr_event, but at that point we've already freed the
AF_INET/AF_INET6 if_afdata pointers.
In other words: when the iflladdr_event callbacks fire we can't assume
that ifp->if_afdata[AF_INET] will be set.
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