Improve windows logs when it comes to iptables

[manuelbuil]

Expected Behavior

Current Behavior

We see the following logs:

I0412 09:55:06.903005    4612 main.go:567] Starting flannel in iptables mode
W0412 09:55:06.903005    4612 iptables_windows.go:39] unimplemented
W0412 09:55:06.903005    4612 main.go:530] no subnet found for key: FLANNEL_IPV6_NETWORK in file: /run/flannel/subnet.env
W0412 09:55:06.903005    4612 main.go:530] no subnet found for key: FLANNEL_IPV6_SUBNET in file: /run/flannel/subnet.env
W0412 09:55:06.903005    4612 iptables_windows.go:50] unimplemented
I0412 09:55:06.903005    4612 kube.go:476] Creating the node lease for IPv4. This is the n.Spec.PodCIDRs: [10.42.2.0/24]

which could be considered alarming by users when reading unimplemented or reading iptables mode even if they are in Windows

Possible Solution

Steps to Reproduce (for bugs)

Context

Your Environment

• Flannel version:
• Backend used (e.g. vxlan or udp):
• Etcd version:
• Kubernetes version (if used):
• Operating System and version:
• Link to your project (optional):