Note: will be good to disable this by udev rule for i40e

Found that in drivers 2.3.6 and newer this should also work:

sudo ethtool --set-priv-flags <interface name> disable-fw-lldp on

This is probably easier, as you do not have to find our the interface ids.
But on Vyos 1.2.5-epa i get:
Cannot set private flags: Operation not supported

This issue exists in firmware 6.8 and 7.1.
Starting with 7.1 i can see that the disable command 'sudo ethtool --set-priv-flags <interface name> disable-fw-lldp on' also works.

I do not have that hardware available, but a possible solution could be the following snippet which could be run on system boot:

for f in /sys/class/net/*; do
    dev=$(basename $f)
    driver=$(readlink $f/device/driver/module)
    if [[ -n $driver ]] && [[ x"$(basename $driver)" -eq x"i40e" ]]; then
        sudo ethtool --set-priv-flags $dev disable-fw-lldp on
    fi
done

@Merijn you could test that? It could be part of /opt/vyatta/sbin/rl-system.init