fix(inputs.ethtool): Check for nil (#12867)

plugins/inputs/ethtool/ethtool_linux.go

@@ -133,11 +133,11 @@ func (e *Ethtool) gatherEthtoolStats(iface NamespacedInterface, acc telegraf.Acc
 	}
 
 	cmdget, err := e.command.Get(iface)
-	if err != nil {
+	// error text is directly from running ethtool and syscalls
+	if err != nil && err.Error() != "operation not supported" {
 		acc.AddError(fmt.Errorf("%q get: %w", iface.Name, err))
 		return
 	}
-
 	for k, v := range cmdget {
 		fields[e.normalizeKey(k)] = v
 	}

plugins/inputs/ethtool/namespace_linux.go

@@ -96,7 +96,10 @@ func (n *NamespaceGoroutine) Get(intf NamespacedInterface) (map[string]uint64, e
 		}, nil
 	})
 
-	return result.(map[string]uint64), err
+	if result != nil {
+		return result.(map[string]uint64), err
+	}
+	return nil, err
 }
 
 // Start locks a goroutine to an OS thread and ties it to the namespace, then