Merge pull request #52569 from tmjd/add-proxy-forward-rules

Automatic merge from submit-queue (batch tested with PRs 55009, 55532, 55601, 52569, 55533). If you want to cherry-pick this change to another branch, please follow the instructions <a href="https://github.com/kubernetes/community/blob/master/contributors/devel/cherry-picks.md">here</a>.

Kube-proxy adds forward rules to ensure NodePorts work

**What this PR does / why we need it**:
Updates kube-proxy to set up proper forwarding so that NodePorts work with docker 1.13 without depending on iptables FORWARD being changed manually/externally.

**Which issue this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close that issue when PR gets merged)*: fixes #39823

**Special notes for your reviewer**:
@thockin I used option number 2 that I mentioned in the #39823 issue, please let me know what you think about this change.  If you are happy with the change then I can try to add tests but may need a little direction about what and where to add them.

**Release note**:

```release-note
Add iptables rules to allow Pod traffic even when default iptables policy is to reject.
```

pkg/util/iptables/iptables.go

@@ -91,6 +91,7 @@ const (
 	ChainPrerouting  Chain = "PREROUTING"
 	ChainOutput      Chain = "OUTPUT"
 	ChainInput       Chain = "INPUT"
+	ChainForward     Chain = "FORWARD"
 )
 
 const (