Describe the bug
iptables script does not redirect users with group ID equals the number specified with -u option.
https://github.com/istio/istio/blob/master/tools/deb/istio-iptables.sh#L265

Expected behavior
I am expecting only the user whose user ID specified with -u is not affected by the iptables redirection.

Steps to reproduce the bug
Given two users: user-a and user-b:
username | user-id | group-id
user-a | 5001 | 8001
user-b | 8001 | 9001
If I evoke the script with: "sudo ./istio-iptables.sh -u 8001 -i '*' -p 15001", then both user-a and user-b will not be intercepted.

Version
I was using the iptables script alone on a VM.

Is Istio Auth enabled or not?
Not relavent.

Environment
A GCE VM with image "Google Drawfork Debian GNU/Linux 9"