Takes the same approach as when adding a new address - we no longer
announce the new lladdr right away but we announce the result.
This will either be RTM_ADD or RTM_MISS.
RTM_DELETE is only sent if we have a lladdr assigned OR gc'ed.
This tells us when a new lladdr has been added (RTM_ADD),
changed (RTM_CHANGE), deleted (RTM_DELETED) or has failed to been
resolved (RTM_MISS). The latter case can be interpreted as unreachable.
a07ba9f67e