Nowadays, users should use the standard "PropertiesChanged" signal
on "org.freedesktop.DBus.Properties" interface.
(cherry picked from commit 6fb917178a)
(cherry picked from commit 98773bff54)
Many different interface types can support VLANs, including
Infiniband, WiFi, etc. So we have to create a new device class
for them instead of keeping the support in NMDeviceEthernet.