'cannot lint path-mtu' false positive when global-physnet-mtu is used instead

[Andrea Ieri]

From the charm config documentation:

    path-mtu:
      Default: null
      Description: |
        Maximum size of an IP packet (MTU) that can traverse the
        underlying physical network infrastructure without fragmentation
        when using an overlay/tunnel protocol. This option allows
        specifying a physical network MTU value that differs from the
        default global-physnet-mtu value.
      Type: int

In a simple cloud where the overlay network uses mtu 9000 the simplest (and valid) config is to set global-physnet-mtu to 9000 and leave path-mtu unset.

In such a scenario juju-lint will produce the following false positive:

[WARNING] [/tmp/openstack-bundle.yaml] [manual/manual] Application neutron-api has no config for 'path-mtu', cannot determine if == 9000.

[Gabriel Cocenza (gabrielcocenza)]

I think in that case it's a question of creating a new rules file for the simple cloud.
bug 1988851 is setting global-physnet-mtu to 9000 and path-mtu >= 1558 for ovn and path-mtu >= 1550 for ovs.