wake-on: g bit doesn't update status on eth0

[Victor]

Environment: pi3 + network-manager snap (stable 165) and connected with an eth cable

STEPS

1. Setup candidate core image on pi3

2. Install: $ snap install --beta canonical-se-engineering-tests && snap install --candidate network-manager && snap install --devmode --edge se-test-tools

3. Check the ethernet port for the wake-on-lan setting (eth0 in this case)
  $ sudo se-test-tools.ethtool eth0

Verification:

The output should be similar to this:
Settings for eth0:
 [...]
 Supports Wake-on: pumbg
 Wake-on: g
 [...]

The relevant line is the "Wake-on:" one. It should have the value "g"
set which marks the port as waking up on the magic packet.

Current result: wake-on: stays in "d"
Expected result: wake-on: should change to "g" when on eth connection