This indicates the status of reachabilty to the neighbor
on the other end of the Shared-segment.
If the neighbor on the other end is reachable with
matching link-id and different modes, then the status is
NeighborUp.
If the neighbor is not reachable, this status is
NeighborDown.
If the neighbor is reachable, but with the same mode,
then this status is set to Error.