Make Egress work with kube-proxy IPVS strictARP mode

[jianjuns]

Describe the problem/challenge you have
When kube-proxy IPVS is configured with strictARP mode (which is required in particular cases like #3785, #3370), Antrea Egress feature may not work as expected, as described in #3370 (comment).

Describe the solution you'd like
There is already a plan described in a TODO comment of Egress IPAssigner code:

antrea/pkg/agent/ipassigner/ip_assigner_linux.go

Lines 213 to 219 in a87ef55

	// Start the ARP responder only when the dummy device is not created. The kernel will handle ARP requests
	// for IPs assigned to the dummy devices by default.
	// TODO: Check the arp_ignore sysctl parameter of the transport interface to determine whether to start
	// the ARP responder or not.
	if a.dummyDevice == nil && a.arpResponder != nil {
	go a.arpResponder.Run(ch)
	}

. Basically, we should let Egress use Antrea ARP responder to respond to ARP for Egress IPs.

@xliuxu @tnqn

[xliuxu]

This should be a simple fix. I will take this. Thank you @jianjuns.

[jsalatiel]

Will this be available on 1.7?

[jianjuns]

Yes. We already merged the fix to main. You can try it if you want.