that depends, who's the origin GW that appears in the logs?
if they are separate, which I believe they are, then you need to write all of them, as in the sk's example ("GW1,GW2,GW3")
cp_log_export set name <name> filter-origin-in "GW1,GW2,GW3"
You can verify in the FilterConfiguration.xml that there's an OR in that field (origin) with all your matching values. Should look like that:
<field name="origin" operator="or">
<value operation="eq">GW1</value>
<value operation="eq">GW2</value>
<value operation="eq">GW3</value>
</field>