Raspberry Pi 3: NetworkManager doesn't change connection state on ethernet cable disconnection

[Francesco Meli]

I'm testing NetworkManager using 2 keyfile:
one keyfile for the wired connection and one keyfile for the wireless connection.

- The setup works great on Raspberry Pi 1 and Raspberry pi 2 and the 2 connection states (checked using `nmcli d` command) follow the actual state of the connection (plug/unplug eth cable, turn on/off wifi router)
- On Raspberry Pi 3 the Manager is behaving incorrectly.
- I'm doing my tests by moving the very same SD card from one raspberry to another.

On Pi 3 the behavior is the following:

- If the Raspberry is booted up WITH the ethernet cable connected and then after the boot I unplug the cable, the status of the ethernet (checked using `nmcli d` command) connection remains connected and there is no way to make it change state.

- On the other hand if the Raspberry is booted up WITHOUT the ethernet cable connected and after the boot i plug it in/out repeatedly, the state of the connection (checked using `nmcli d` command) follows accordingly.

I also tried to use NetworkManager with ifupdown plugin instead of keyfile plugin.

The behavior is exactly the same:

- If I boot up the RasPi 3 with cable disconnected everything works perfect.
- If I boot up the RasPi 3 with cable connected NetworkManager doesn't recognize the cable disconnection event.

The command nmcli d returns the following output:
NAME: ifupdown (eth0)
UUID: ...
TYPE: 802-3-ethernet
DEVICE: eth0

Atacched the journal.

[Tony Espy (awe)]

This bug list is meant to track issues with snaps maintained in this project (meant for usage on Ubuntu Core only). If you have issues with NetworkManager on Ubuntu Desktop, please use the Ubuntu network-manager bug list: https://bugs.launchpad.net/ubuntu/+source/network-manager.

If this bug does involve the network-manager snap and Ubuntu Core, please provide the relevant details (i.e. snap version, Ubuntu Core version, ...).