Comment 15 for bug 2037667

This seems to do the trick using the following Netplan config as a testcase.

All 3 interfaces (tun[0-2]) are correctly created with their local & remote properties set:

root@jj-abi:~/systemd# ip link show dev tun0
19: tun0@NONE: <NOARP,UP,LOWER_UP> mtu 1448 qdisc noqueue state UNKNOWN mode DEFAULT group default qlen 1000
    link/gre6 fe80::1 brd 2001:dead:beef::2 permaddr e262:75ae:2aa0::
root@jj-abi:~/systemd# ip link show dev tun1
20: tun1@NONE: <NOARP,UP,LOWER_UP> mtu 1332 qdisc noqueue state UNKNOWN mode DEFAULT group default qlen 1000
    link/tunnel6 fe80::2 brd 2001:dead:beef::3 permaddr c2aa:7446:cc29::
root@jj-abi:~/systemd# ip link show dev tun2
21: tun2@NONE: <NOARP,UP,LOWER_UP> mtu 1444 qdisc noqueue state UNKNOWN mode DEFAULT group default qlen 1000
    link/gre6 fe80::3 brd 2001:dead:beef::4 permaddr 3ef2:274c:a921::

Netplan test config:
```
network:
  version: 2
  tunnels:
    tun0:
      mode: ip6gre
      local: fe80::1
      remote: 2001:dead:beef::2
    tun1:
      mode: vti6
      local: fe80::2
      remote: 2001:dead:beef::3
    tun2:
      mode: ip6gre
      key: 1234
      local: fe80::3
      remote: 2001:dead:beef::4
```