Using The Dude, add a new probe like:
With OID:
iso.org.dod.internet.mgmt.mib-2.interfaces.ifTable.ifEntry.ifSpeed.1
Some routers will have a different OID. For example, HAP AC2 uses
iso.org.dod.internet.mgmt.mib-2.interfaces.ifTable.ifEntry.ifSpeed.3
for port 1
Add the probe to the device