On Nexcom V110 vni-0/3 is shared with eth-0 since there are only 4 NICs available

So if you need to change the speed of this port, you would need to execute it on the ubuntu shell – using the below

sudo ethtool -s eth 0 speed 100 duplex full autoneg off 

You can then check the new speed setting using the below

ethtool eth0

The below output will continue to show 1gbps/full but the actual speed would be what is seen in the ethtool output above

You can also change the mode to make eth0 a full wan port (no longer a management port) using the below