Comment 12 for bug 1938920

Thank you for the comments Łukasz, I'll keep them in mind for next time.

For Hirsute:
I tested netplan.io 0.103-0ubuntu5~21.04.1 and attached the official autopkgtest logs, all passed. The initramfs-tools/0.139ubuntu3 (amd64) reverse dependency test passed as well after a re-try.

Also I verified that we do not display an deprecation error if the (legacy) gateway4/6 field are being used:
```
root@hh:~# dpkg -l | grep netplan
ii libnetplan0:amd64 0.103-0ubuntu5~21.04.1
ii netplan.io 0.103-0ubuntu5~21.04.1
root@hh:~# netplan set ethernets.eth0.gateway4=1.2.3.4
root@hh:~# netplan set ethernets.eth0.gateway6=beef::42
root@hh:~# netplan get
network:
  ethernets:
    eth0:
      dhcp4: true
      gateway4: 1.2.3.4
      gateway6: beef::42
  version: 2
root@hh:~# netplan apply
```

For Focal:
I tested netplan.io 0.103-0ubuntu5~20.04.1 and attached the official autopkgtest logs, all passed.

Also I verified that we do not display an deprecation error if the (legacy) gateway4/6 field are being used:
```
root@ff:~# dpkg -l | grep netplan
ii libnetplan0:amd64 0.103-0ubuntu5~20.04.1
ii netplan.io 0.103-0ubuntu5~20.04.1
root@ff:~# netplan set ethernets.eth0.gateway4=1.2.3.4
root@ff:~# netplan set ethernets.eth0.gateway6=beef::42
root@ff:~# netplan get
network:
  ethernets:
    eth0:
      dhcp4: true
      gateway4: 1.2.3.4
      gateway6: beef::42
  version: 2
root@ff:~# netplan apply

```