determine online/offline status from local copy of close_node_changes

any node being out of the close node range considered as offline
regarding question of a) : I don't know where the majec number of EIGHT comes from. IMO I think some consistency of using static parameters shall be followed.
However, if there is good reason to use EIGHT or decided to use this majec number, I can update the code.

regarding question of b) : the order of nodes indicates the insertion time, and the first means it is the oldest. as we are talking about offline nodes, so I think the oldest shall be pruned.
the previous design using distance and the furthest will be pruned, however Prakash said it is not required so changed to this way.