Tweak kernel ARP settings for keepalived to work.

[meisterT]

This has not been necessary in the past, but was required at ICPC WFs in Egypt, see also:
https://keepalived.readthedocs.io/en/latest/software_design.html#note-on-using-vrrp-with-virtual-mac-address

[meisterT]

cc @eldering

Not sure whether we want this in general

[vmcj]

This now depends on the CLUSTER_ID which is something we probably don't want to keep.

[nickygerritsen]

This now depends on the CLUSTER_ID which is something we probably don't want to keep.

We should add a conditional for this I guess, since we only need these three when we have a cluster. But then again, we only have keepalived when we have a cluster right?

[vmcj]

This now depends on the CLUSTER_ID which is something we probably don't want to keep.

We should add a conditional for this I guess, since we only need these three when we have a cluster. But then again, we only have keepalived when we have a cluster right?

No, CLUSTER_ID is for the keepalived cluster, in a hypothetical case you have a network blue with 4 domservers where 2 replicate with each other (let's call them wf46 & wf47) than they would use the same mac in both clusters and you get 50% of the packets because the same mac exists. So its only related to how many distinct keepalived clusters you run on the same network. So it could be useful when pc2 also does keepalived for example.