Routing table metrics issues

[kdeme]

Two bugs / issues related to the routing_table_nodes metric of routing_table.nim:

• The counting with seen label is off. TBI
• Routing table can be used by several protocols with DHT, and thus instantiated multiple times, however the counting will all sum up. Probably have to add some identifier to the routing table object and use that in a label.

Additionally the current way the state label is used is probably confusing (all nodes vs seen nodes)