Promote feature CleanupStaleUDPSvcConntrack from Alpha to Beta

[hongliangl]

In #5112, due to the limitations of the Go netlink library, AntreaProxy
would unconditionally delete conntrack entries added by kube-proxy in
conntrack zone 0. AntreaProxy was supposed to only delete its own entries
in conntrack zones 65520 or 65521. To address this, a feature was added
to isolate the relevant code.

After the merge of #6193, the netlink library was updated, allowing
AntreaProxy to precisely delete conntrack entries in zones 65520 or 65521.
It is now safe to enable the corresponding code by default.

Depends on #6379

[antoninbas]

Are we planning to bump this up to GA for v2.2?
With the current state of things, is there any situation where a user would want to be able to disable this functionality?

(You may to update some unit tests with this change)

[hongliangl]

Are we planning to bump this up to GA for v2.2?

I think we can do it in v2.2. After all, this is a basic functionality. It was not supposed to add a feature gate when adding this. However, due to the limitation of netlink, we had to add a feature gate in #5112.

With the current state of things, is there any situation where a user would want to be able to disable this functionality?

Maybe there is no reason to disable the functionality since it is a very basic. You can find the corresponding e2e tests in this link https://github.com/kubernetes/kubernetes/master/test/e2e/network/conntrack.go.

(You may to update some unit tests with this change)

Yes, I'll add or update some unit tests to cover all code of the functionality.

[tnqn]

I see you already extracted virtualNodeIP related cleanup to #6379, which is the right thing. The PR should just focus on the promotion.

[hongliangl]

I see you already extracted virtualNodeIP related cleanup to #6379, which is the right thing. The PR should just focus on the promotion.

I should mention that the fix #6372 should be merged first, and this pr can be merged then.

[antoninbas]

could we extract the refactoring of pkg/agent/proxy/proxier_test.go from this graduation PR? Are the 2 changes inter-dependent?

[hongliangl]

could we extract the refactoring of pkg/agent/proxy/proxier_test.go from this graduation PR?

Will do.

Are the 2 changes inter-dependent?

No, the refactoring of pkg/agent/proxy/proxier_test.go could be dependent. Though my original motivation for refactoring the file is to enable CleanupStaleUDPSvcConntrack in some tests.

[antoninbas]

LGTM

[hongliangl]

/test-all

[tnqn]

LGTM