usernetes: VXLAN doesn't seem to work on GCP (while works on AWS and Azure); probably related to MTU

VXLAN doesn’t seem to work on GCP, while it works on AWS and Azure

$ kubectl taint nodes --all node-role.kubernetes.io/control-plane-
$ ./hack/test-smoke.sh 
[INFO] Waiting for nodes to be ready
node/u7s-suda-tmp-1 condition met
node/u7s-suda-tmp-2 condition met
[INFO] Creating StatefulSet "dnstest" and headless Service "dnstest"
service/dnstest created
statefulset.apps/dnstest created
[INFO] Waiting for 3 replicas to be ready
Waiting for 3 pods to be ready...
Waiting for 2 pods to be ready...
Waiting for 2 pods to be ready...
Waiting for 1 pods to be ready...
Waiting for 1 pods to be ready...
partitioned roll out complete: 3 new pods have been updated...
[INFO] Connecting to dnstest-{0,1,2}.dnstest.default.svc.cluster.local
If you don't see a command prompt, try pressing enter.
wget: bad address 'dnstest-0.dnstest.default.svc.cluster.local'
pod "dnstest-shell" deleted
pod default/dnstest-shell terminated (Error)

Likely to be related to MTU.

• GCP: 1460
• AWS: 9001
• Azure: 1500

Version: Usernetes gen2-v20230906.0, Rootless Docker 24.0.6, on Ubuntu 22.04.