Try and fix twin brother switch detection (#329)

cmd/metal-api/internal/service/switch-service.go

@@ -363,15 +363,15 @@ func (r *switchResource) registerSwitch(request *restful.Request, response *rest
 // replaceSwitch replaces a broken switch
 //
 // assumptions:
-//  - cabling btw. old, new and twin-brother switch in the same rack is "the same" (m1 is connected to swp1s0 at every switch)
+//   - cabling btw. old, new and twin-brother switch in the same rack is "the same" (m1 is connected to swp1s0 at every switch)
 //
 // constraints:
-//  - old, new and twin-brother switch must have the same partition and rack
-//  - old switch needs to be marked for replacement
-//  - twin-brother switch must not be marked for replacement (otherwise there would be no valid source of truth)
-//  - new switch needs all the nics of the twin-brother switch
-//  - new switch gets the same vrf configuration as the twin-brother switch based on the switch port name
-//  - new switch gets the same machine connections as the twin-brother switch based on the switch port name
+//   - old, new and twin-brother switch must have the same partition and rack
+//   - old switch needs to be marked for replacement
+//   - twin-brother switch must not be marked for replacement (otherwise there would be no valid source of truth)
+//   - new switch needs all the nics of the twin-brother switch
+//   - new switch gets the same vrf configuration as the twin-brother switch based on the switch port name
+//   - new switch gets the same machine connections as the twin-brother switch based on the switch port name
 func (r *switchResource) replaceSwitch(old, new *metal.Switch) error {
 	twin, err := r.findTwinSwitch(new)
 	if err != nil {
@@ -403,6 +403,9 @@ func (r *switchResource) findTwinSwitch(newSwitch *metal.Switch) (*metal.Switch,
 		if sw.PartitionID != newSwitch.PartitionID {
 			continue
 		}
+		if sw.Mode == metal.SwitchReplace || sw.ID == newSwitch.ID {
+			continue
+		}
 		if twin == nil {
 			twin = &sw
 		} else {