Automatic merge from submit-queue. 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>.
Cleanup of ipvs utils
**What this PR does / why we need it**:
This PR is a small cleanup of pkg/util/ipvs.
The changes are as follows:
1. Rename toBackendService -> toIPVSService and toBackendDestination -> toIPVSDestination. The use of the term 'backend' makes things really confusing and this renamig makes it more explicit about what we are doing.
2. Give the libnetwork/ipvs package the name libipvs. This makes it less confusing since the package these files are in is also ipvs.
3. Some variable naming cleanup to make things easier to read.
/assign @m1093782566
**Release note**:
```release-note
None
```
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