fix: Support switching from loadbalancer to externalName for services

[nilo19]

What type of PR is this?

/kind bug

What this PR does / why we need it:

Fix two issues when changing service type from lb to externalName.

1. ExternalName service has no ipFamilies, we should not panic this.
2. We should not use v4Enabled, v6Enabled := getIPFamiliesEnabled(service) to check what backend pools should be deleted from the vmss.

Which issue(s) this PR fixes:

Fixes #7503

Special notes for your reviewer:

Does this PR introduce a user-facing change?

fix: Support switching from loadbalancer to externalName for services

Additional documentation e.g., KEPs (Kubernetes Enhancement Proposals), usage docs, etc.:

[nilo19]

/retest

[feiskyer]

Thanks for the fix.

/lgtm

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: feiskyer, nilo19

The full list of commands accepted by this bot can be found here.

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Needs approval from an approver in each of these files:

• OWNERS [feiskyer,nilo19]

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[nilo19]

/retest

[MartinForReal]

/retest

[nilo19]

/test pull-cloud-provider-azure-e2e-ccm-vmss-multi-slb-capz

[nilo19]

/cherrypick release-1.31

[nilo19]

/cherrypick release-1.30

[nilo19]

/cherrypick release-1.29

[nilo19]

/cherrypick release-1.28

[k8s-infra-cherrypick-robot]

@nilo19: new pull request created: #7565

In response to this:

/cherrypick release-1.31

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes-sigs/prow repository.

[k8s-infra-cherrypick-robot]

@nilo19: new pull request created: #7566

In response to this:

/cherrypick release-1.30

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes-sigs/prow repository.

[k8s-infra-cherrypick-robot]

@nilo19: #7518 failed to apply on top of branch "release-1.29":

Applying: fix: Support switching from loadbalancer to externalName for services
Using index info to reconstruct a base tree...
M	pkg/provider/azure_loadbalancer.go
M	pkg/provider/azure_loadbalancer_test.go
M	pkg/provider/azure_privatelinkservice.go
M	pkg/provider/azure_utils.go
M	pkg/provider/azure_utils_test.go
M	pkg/provider/azure_vmss.go
Falling back to patching base and 3-way merge...
Auto-merging pkg/provider/azure_vmss.go
Auto-merging pkg/provider/azure_utils_test.go
Auto-merging pkg/provider/azure_utils.go
Auto-merging pkg/provider/azure_privatelinkservice.go
CONFLICT (content): Merge conflict in pkg/provider/azure_privatelinkservice.go
Auto-merging pkg/provider/azure_loadbalancer_test.go
Auto-merging pkg/provider/azure_loadbalancer.go
CONFLICT (content): Merge conflict in pkg/provider/azure_loadbalancer.go
error: Failed to merge in the changes.
hint: Use 'git am --show-current-patch=diff' to see the failed patch
hint: When you have resolved this problem, run "git am --continue".
hint: If you prefer to skip this patch, run "git am --skip" instead.
hint: To restore the original branch and stop patching, run "git am --abort".
hint: Disable this message with "git config advice.mergeConflict false"
Patch failed at 0001 fix: Support switching from loadbalancer to externalName for services

In response to this:

/cherrypick release-1.29

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes-sigs/prow repository.

[k8s-infra-cherrypick-robot]

@nilo19: #7518 failed to apply on top of branch "release-1.28":

Patch is empty.
hint: When you have resolved this problem, run "git am --continue".
hint: If you prefer to skip this patch, run "git am --skip" instead.
hint: To record the empty patch as an empty commit, run "git am --allow-empty".
hint: To restore the original branch and stop patching, run "git am --abort".
hint: Disable this message with "git config advice.mergeConflict false"

In response to this:

/cherrypick release-1.28

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes-sigs/prow repository.