Please note - you may want to validate whether the options used affect your setup.
Create a new service file.
nano /etc/systemd/system/disable-offloading.service
Paste the required information/command in the newly created service file - please change eth0 to your desired adapter.
[Unit]
Description=Disable NIC offloading
After=network.target
[Service]
Type=oneshot
ExecStart=/sbin/ethtool -K eth0 gso off gro off tso off tx off rx off rxvlan off txvlan off sg off
RemainAfterExit=true
[Install]
WantedBy=multi-user.target
Load the new service file and enable on reboot.
systemctl daemon-reexec && systemctl daemon-reload && systemctl enable disable-offloading.service
I solved it here: with post-up command
root@proxmox43:~# cat /etc/network/interfaces
auto lo
iface lo inet loopback
iface eno1 inet manual
auto vmbr0
iface vmbr0 inet static
address 192.168.1.43/24
gateway 192.168.1.1
bridge-ports eno1
post-up /sbin/ethtool -K eno1 tx off rx off
bridge-stp off
bridge-fd 0