It’s a standard mirroring setup as required for full network monitoring with tools like Wireshark (see http://wiki.wireshark.org/CaptureSetup/Ethernet#Capture_using_a_monitor_mode_of_the_switch).
The idea is that you normally can’t monitor all network traffic on one computer on a multi-device LAN, because not all traffic makes it to that computer. To get around that, you can configure one port on your switch to be a mirror port, so that all traffic that passes through the switch is echoed to that mirror port. Then you connect that port to a separate port on your monitoring PC, and configure Wireshark, Networx, nLive, SmartSniff, Snort, etc. to look only at that port. It’s extremely powerful.
On the other hand, Glasswire seems to be more about traffic on individual machines (and related to processes) than it is about all LAN traffic. In which case it would be helpful if I could make sure Glasswire is NOT looking at the monitor port. Hence the request for a setting.