Remove Topology's port_status/state_notify event filter entry from Network DSL .conf file

[y-higuchi]

Use event forwarding API

[yasuhito]

👍

[y-higuchi]

TODO:

1. Use event forwarding API (Add Event Forwarding Interfaces to switch daemon/manager trema/trema#258) when they are merged to trema mainline.
2. submit separate PR for topology C API first.