Should not use loopback addresses

[hzxuzhonghu]

fixes: istio/istio#17261

[hzxuzhonghu]

/cherry-pick release-1.3

[istio-testing]

@hzxuzhonghu: new pull request created: #5044

Details

In response to this:

/cherry-pick release-1.3

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[albatross0]

@hzxuzhonghu
It does not work.
Linux kernel returns ENETUNREACH if the destination address of the TCP connection is a multicast address.

$ kubectl exec --context=$CTX_CLUSTER1 $SLEEP_POD -n foo -c sleep -- curl -I httpbin.bar.global:8000/headers
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
  0     0    0     0    0     0      0      0 --:--:-- --:--:-- --:--:--     0curl: (7) Couldn't connect to server
command terminated with exit code 7

[hzxuzhonghu]

Thanks for the report@albatross0

[hzxuzhonghu]

multicast address can not be used, as by default there is no route to these address.
we should use class E addresses 240.0.0.0 ~ 255.255.255.254, which is preserved for future use