[VOL-1697] Update Admin state

This commit consists of the following:
1) Update the Admin State logic to remove any dependencies
2) Update the device state machine to handle the changed admin state
transitions
3) Allow the core to update its internal memory before sending a
reponse to child device detection.

Change-Id: Ifa20ad4d4b36425b672095e2055424bbf05e34bb
diff --git a/rw_core/coreIf/device_manager_if.go b/rw_core/coreIf/device_manager_if.go
index 367f442..d2e6356 100644
--- a/rw_core/coreIf/device_manager_if.go
+++ b/rw_core/coreIf/device_manager_if.go
@@ -34,4 +34,5 @@
 	DeleteLogicalPorts(cDevice *voltha.Device) error
 	DeleteAllChildDevices(cDevice *voltha.Device) error
 	RunPostDeviceDelete(cDevice *voltha.Device) error
+	MarkChildDevicesAsUnReachable(cDevice *voltha.Device) error
 }