Comment 1 for bug 1988851

To be more precise, it can be bigger than 1550 or 1558, but to use mtu=1500 on tenant networks, those two values are the requirement.

Using bigger value can be a problem especially with OVN when communicating with other external networks through a router because of missing:
https://bugs.launchpad.net/charm-neutron-api-plugin-ovn/+bug/1947391