nixos/networkd: Disable bond0 creation by bonding driver

Linux defaults to creating a `bond0` interface when modprobing the
`bonding` driver, because the `max_bonds` option defaults to `1`¹.

This `bond0` interface is created with the default bond mode
`balance-rr`, which is most often undesirable.
Networkd in turn is unable to change this mode, since it does not
implement netdev recreation on parameter mismatch².

If we instead default `max_bonds=0` the driver will be loaded, but no
default interface will be created, leaving networkd in a better position
to set up the network configuration.

[1] https://www.kernel.org/doc/Documentation/networking/bonding.txt
[2] systemd/systemd#9627

Co-Authored-By: Graham Christensen <graham@grahamc.com>

nixos/modules/system/boot/networkd.nix

@@ -1753,6 +1753,10 @@ in
 
     (mkIf config.systemd.network.enable {
 
+      boot.extraModprobeConfig = ''
+        options bonding max_bonds=0
+      '';
+
       users.users.systemd-network.group = "systemd-network";
 
       systemd.additionalUpstreamSystemUnits = [