The TLS Mode Field is not Being Defaulted

[danehans]

What happened:
The gateway.spec.tls.mode field is not being defaulted.

What you expected to happen:
The field set to "Terminate" (i.e. the default) when unspecified.

How to reproduce it (as minimally and precisely as possible):

• cat examples/wildcard-https.yaml
• make install
• kubectl get gateways/gateway -o yaml

Anything else we need to know?:
Other fields that should be defaulted may be effected by this bug.

[danehans]

The TLS mode is unspecified:

$ cat examples/wildcard-https.yaml 
kind: Gateway
...
    tls:
      options: {}
      certificateRef:
        name: example-wildcard
        kind: Secret
        group: core
    ...

The mode should be set to "Terminate" (default) but it's nil:

$ kubectl get gateways/gateway -o yaml
apiVersion: networking.x-k8s.io/v1alpha1
kind: Gateway
...
    tls:
      certificateRef:
        group: core
        kind: Secret
        name: example-wildcard
      options: {}
      routeOverride:
        certificate: Deny
...