So if you want only specific ports one way (could be that there is another one) is to create a port group.
In Netsight Console in the device tree right click on "my Network" and choose "add device group" and for this example let's name it "PortGroup1".
Then click on the switch that you want to add ports from and in the ïnterface summary" select all the ports that you want in your alarm group.
i.e. I've selected ports ge.1.1-12
Then right click on the ports that you've selected and click "add port elements to group" and select the PortGroup1.
The next step is to configure the Alarm Manager to only report a link down of PortGroup1.
So go to the Alarm Manager and select "link down" in the Alarm table.
On the bottom of the window in the "Additional Criteria" section click on Device Groups and select PortGroup1.
As I've mentioned before make sure that the trap receiver is set correcty so the switch forwards the traps to Netsight.
In my lab with my G&D series switches it worked so I hope that is the same with the X series.