op-mode: T3619: bugfix "show interfaces" for VLANs
op-mode: T3619: bugfix "show interfaces" for VLANs

Commit 31169fa8a7 ("vyos.ifconfig: T3619: only set offloading options if
supported by NIC") always instantiated an object of the Ethtool class for an
ethernet object - this is right as a real ethernet interface is managed by
Ethtool.

Unfortunately the script used for "show interface" determindes the "base class"
for an interface by its name, so eth0 -> Ethernet, eth0.10 -> Ethernet. This
assumption is incorrect as a VLAN interface can not have the physical parameters
changed of its underlaying interface. This can only be done for eth0.

There is no need for the op-mode script to determine the implementation class
for an interface at this level, as we are only interested in the state of the
interface and it's IP addresses - which is a common operation valid for every
interface on VyOS.

vyos/vyos-1x,vyos/vyos-1x,vyos/vyos-1x,vyos/vyos-1x