Hello @Raz
I respect what you are trying to do and encourage your project. That being said, port mirroring capability on the GX20 is currently not an available feature, and would not be an ideal task for a firewall to perform. Typically, this behavior is configured on a switch. The GX20 performance would suffer significantly if it were to copy every frame to a mirror destination, and most firewalls try to handle IDS themselves instead of copying the frames elsewhere for inspection (or perhaps there is an inline IDS filter).
The GS product line of switches also does not support port mirroring.
Instead of mirroring traffic, is it possible that your IDS use more than one interface and bridge the traffic between them? This would allow the traffic to pass through the IDS filter CPU for inspection, and still make it from say the access point up to the GX20.