Our current examples of OVN Kubernetes secondary networks have 2 MTU-related issues:

1. The layer 2 overlay example uses MTU 1300, although with default it could go up to 1400. Since many customers simply copy-paste documented examples, we should either use the typical maximum in the docs, or to remove this MTU field altogether and rely on OVN's default, which is 1400.
2. The localnet topology example does not specify any MTU. Due to that, it defaults to 1400, which is wasteful for localnet, since it can go (in the typical setup) up to 1500.

4.16

Docs

1. Go to https://docs.openshift.com/container-platform/4.16/virt/vm_networking/virt-connecting-vm-to-ovn-secondary-network.html

"Creating a NAD for layer 2 topology using the CLI" mentions MTU 1300.
"Creating a NAD for localnet topology using the CLI" mentions no MTU.

"Creating a NAD for layer 2 topology using the CLI" mentions MTU 1400 or nothing.
"Creating a NAD for localnet topology using the CLI" mentions MTU 1500.