cmd, eth, p2p, p2p/discover: init and clean up the seed cache

p2p/discover/node.go

@@ -387,3 +387,7 @@ func (db *nodeDB) add(id NodeID, addr *net.UDPAddr, tcpPort uint16) *Node {
 	db.update(n)
 	return n
 }
+
+func (db *nodeDB) close() {
+	db.ldb.Close()
+}