Automatic merge from submit-queue (batch tested with PRs 52520, 52033, 53626, 50478). 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>.

Fix kube-proxy to use proper iptables commands for IPv6 operation

For iptables save and restore operations, kube-proxy currently uses
the IPv4 versions of the iptables save and restore utilities
(iptables-save and iptables-restore, respectively). For IPv6 operation,
the IPv6 versions of these utilities need to be used
(ip6tables-save and ip6tables-restore, respectively).

Both this change and PR #48551 are needed to get Kubernetes services
to work in an IPv6-only Kubernetes cluster (along with setting
'--bind-address ::0' on the kube-proxy command line. This change
was alluded to in a discussion on services for issue #1443.

fixes #50474



**What this PR does / why we need it**:
This change modifies kube-proxy so that it uses the proper commands for iptables save and
iptables restore for IPv6 operation. Currently kube-proxy uses 'iptables-save' and 'iptables-restore'
regardless of whether it is being used in IPv4 or IPv6 mode. This change fixes kube-proxy so
that it uses 'ip6tables-save' and 'ip6tables-restore' commands when kube-proxy is being run
in IPv6 mode.

**Which issue this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close that issue when PR gets merged)*: fixes #50474

**Special notes for your reviewer**:

**Release note**:

```release-note NONE
```