ship default link config to disable systemd link mac-policy

ship default link config to disable systemd link mac-policy

since debian 11, systemd is changing behaviour of MAC address of
bridge, but also bond, where the mac is generated randomly instead
inherit from the first slave.

We tried to fix that with ifupdown2, but that seems to produce some
regressions and independent of that there was still another problem.
Namely, if a bridge don't have any slaves, systemd is keeping bridge
offline.

https://www.justinsteven.com/posts/2023/03/26/virtualbox-bridge-ports-none-no-carrier-debian-11/

That mean that a dhcp daemon like kea can't bind on a standalone
bridge (used for s-nat for example), until a tap interface is started.

So, set up a systemd link config to disable the systemd mac policy by
default (this don't break already fixed ifupdown2 mac).

Funnily CentOS && Fedora also disable it already:
https://fedoraproject.org/wiki/Changes/MAC_Address_Policy_none
https://gitlab.com/redhat/centos-stream/rpms/systemd/-/blob/c8953519504bf2e694bfbc2b02a456c1056f252e/0028-udev-net-setup-link-change-the-default-MACAddressPol.patch#L43

Before this patch:
```
~ ip a sh dev vmbr1
vmbr1: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue state DOWN group default qlen 10
```

After this patch:
```
~ ip a sh dev vmbr1
vmbr1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UNKNOWN group default qlen 1000
```

Signed-off-by: Alexandre Derumier <alexandre.derumier@groupe-cyllene.com>
 [ TL: move to /usr/lib/.. where distro files belong and add comment ]
Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>