Ensure kube-proxy waits for the services/endpointslices informer
caches to be synced *and* all pre-sync events delivered before
setting isInitialized=true. Otherwise, in clusters with many services,
some services may be missing from svcPortMap when kube-proxy starts
(e.g. during daemonset rollout). This can cause kube-proxy to temporarily
remove service DNAT rules and then skip cleanup of UDP conntrack entries
to a service VIP.
Resolves: https://github.com/kubernetes/kubernetes/issues/126468
f520ede814