Fix bug, could delete subnetset when there are still stale subnetport…

[zhengxiexie]

When there are stale subnetports in one subnet of subnetset, we should not allow deleting it.
Tests done:

apiVersion: nsx.vmware.com/v1alpha1
kind: SubnetPort
metadata:
  name: pod-59
  namespace: zx-test-2
spec:
  subnetSet: pod-default

create subnetport and delete pod-default, it will fail reporting

2024-07-15 03:30:04.994	INFO	subnetset/subnetset_controller.go:57	reconciling subnetset CR	{"subnetset": {"name":"pod-default","namespace":"zx-test-2"}}
2024-07-15 03:30:04.994	ERROR	subnetset/subnetset_controller.go:122	deletion failed, delete all the subnetports first	{"subnetset": {"name":"pod-default","namespace":"zx-test-2"}, "error": "stale subnet ports found while deleting subnetset zx-test-2/pod-default"}
2024-07-15 03:30:05.034	INFO	subnetset/subnetset_controller.go:204	updated SubnetSet	{"Name": "pod-default", "Namespace": "zx-test-2", "New Conditions": [{"type":"Ready","status":"False","lastTransitionTime":"2024-07-15T03:30:04Z","reason":"SubnetNotReady","message":"stale subnet ports found while deleting subnetset zx-test-2/pod-default"}]}
2024-07-15 03:30:05.034	DEBUG	recorder/recorder.go:104	stale subnet ports found while deleting subnetset zx-test-2/pod-default	{"type": "Warning", "object": {"kind":"SubnetSet","namespace":"zx-test-2","name":"pod-default","uid":"779fb1b6-50c5-49cf-b870-04e6ea6f13c7","apiVersion":"nsx.vmware.com/v1alpha1","resourceVersion":"1897779"}, "reason": "FailUpdate"}

delete vm-default will succeed since it has no port attached in it.