make network ID configurable for testing

router/java/src/net/i2p/router/Router.java

router/java/src/net/i2p/router/StatisticsManager.java

...er/networkdb/kademlia/FloodfillNetworkDatabaseFacade.java

...ter/networkdb/kademlia/KademliaNetworkDatabaseFacade.java

...et/i2p/router/networkdb/kademlia/PersistentDataStore.java

...rc/net/i2p/router/transport/udp/EstablishmentManager.java

...r/java/src/net/i2p/router/transport/udp/UDPTransport.java