libnl2 and earlier do not implement rtnl_link_get_kernel() and
thus we need compat code to determine whether an interface is
a bond or a VLAN. Previously, the VLAN code would simply assert
and cause NM to exit when running with libnl2 or earlier because
the interface type could not be determined.
Carrier checking can be synchronous, like when bringing up the device.
If the carrier changes as a result of the sync carrier state checking,
the code might change state. Unfortunately brining up a device
happens in response to a state change already, and we can't change
state from within handlers for the device state change signal, so
we need to queue up the new state change that results from a
carrier change.
The carrier signal might be delayed a bit, so if we're creating
the device as a result of activating a connection, make sure the
carrier is up-to-date so we can proceed with activation.
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.
