unified function to set sysctl values

[roffe]

and add https://github.com/kubernetes/kubernetes/pull/70530/files

[roffe]

solves #561

[roffe]

@andrewsykim is this in line with what you was thinking?

[andrewsykim]

Was just thinking we just create specific variables for those cases, something like (but not exactly):

var SysctlNotFoundErr := errors.New("sysctl not found")
...
...

But I'm realizing now that in Kubernetes core, they just ignore the error 🤷‍♂️

[ticpu]

I don't know why no one seems to be affected by this, but since arp_ignore is set to 1, all our externalIPs stopped working until we echo 0 > arp_ignore.