[#60] core/netmap: Define interface of current network properties

Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>

pkg/core/netmap/state.go

@@ -0,0 +1,7 @@
+package netmap
+
+// State groups current system state parameters.
+type State interface {
+	// CurrentEpoch returns number of current NeoFS epoch.
+	CurrentEpoch() uint64
+}