networkd/default: keep static configuration if provided

From the documentation[^1]:
> The setting "dhcp" implies "dhcp-on-stop", and "yes" implies "dhcp" and "static".

I would understand that "yes" implies then: "dhcp-on-stop" and "static"

[^1]: https://www.freedesktop.org/software/systemd/man/systemd.network.html

Signed-off-by: Mathieu Tortuyaux <mtortuyaux@microsoft.com>

systemd/network/zz-default.network

@@ -1,6 +1,6 @@
 [Network]
 DHCP=yes
-KeepConfiguration=dhcp-on-stop
+KeepConfiguration=yes
 IPv6AcceptRA=true
 
 [Match]