Setting to ON_QA. I believe this should be fixed in 4.4

Tested and verified in 4.4.0-0.nightly-2020-05-18-164758

[weliang@weliang FILE]$ oc get net-attach-def -o yaml
apiVersion: v1
items:
- apiVersion: k8s.cni.cncf.io/v1
  kind: NetworkAttachmentDefinition
  metadata:
    creationTimestamp: "2020-05-20T20:48:58Z"
    generation: 1
    name: macvlan-bridge
    namespace: test
    resourceVersion: "23440"
    selfLink: /apis/k8s.cni.cncf.io/v1/namespaces/test/network-attachment-definitions/macvlan-bridge
    uid: 7e4114c9-9162-42be-9e47-16f07b501e87
  spec:
    config: '{ "cniVersion": "0.3.0", "type": "macvlan", "master": "eth0", "mode":
      "bridge", "ipam": { "type": "dhcp" } }'
kind: List
metadata:
  resourceVersion: ""
  selfLink: ""
[weliang@weliang FILE]$ oc patch networkattachmentdefinition.k8s.cni.cncf.io macvlan-bridge -p '{"spec":{"config":" " }}' --type=merge
Error from server: admission webhook "multus-validating-config.k8s.io" denied the request: configuration string is not in JSON format

[weliang@weliang FILE]$ oc patch networkattachmentdefinition.k8s.cni.cncf.io macvlan-bridge -p '{"spec":{"config":"{"cniVersion": "0.3.0", "type": "cvlan", "master": "eth", "mode": "bridge", "ipam": { "type": "dhcp" }}"}}' --type=merge
Error from server: Invalid JSON Patch
[weliang@weliang FILE]$

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://access.redhat.com/errata/RHBA-2020:2310