1. Proposed title of this feature request

ADVMSS Support on Configure-OVS Script

2. What is the nature and description of the request?

Advertise Maximum Segment Size (advmss) is a network route setting that can be defined during a Spoke cluster deployment  to avoid MTU fragmentation for inter-site connections without modifying the WAN links/routes in the middle. A Hub cluster can be on site A and workload cluster can be on site B and MTU fragmentation needs to be avoided.

configure-ovs script should be able to copy advmss network route setting in siteconfig/clusterinstance and applied it on the cluster node if Spoke cluster RHCOS supported this setting on nmstate.
advmss supported in  RHCOS package nmstate>=2.2.47 (i.e., 4.16.46+, 4.18.22+, and 4.20.0+)

This can be applicable for Agent Base Installer as well.

Currently configure-ovs script copy network config for the route set in  Siteconfig/clusterinstance and applied it on the cluster nodes but didn't copy and applied advmss setting. 

3. Why does the customer need this? (List the business requirements here)

Solution would be to update the MTU of the WAN link connecting two sites.
However, customer are often not able to change the MTU of their WAN links. Some customers networks may not easily want to support/accept bigger than 1500 MTU, because the WAN links are not in full control of the telco operator/department, there could be leased WAN links. And in some site routers they do not support bigger values than 9008 in the site router; 9008 as biggest supported MTU is quite common in site routers.

(Also note that decreasing the Machine Network MTU from 9100 is not an option.)
advmss set in a network route config in the siteconfig/clusterinstance is needed as below to unblock deployment issue (inspection, provisioning ...)

              routes:
                config:
                  - destination: 0.0.0.0/0
                    next-hop-address: 192.168.121.1
                    next-hop-interface: infra-bond.121
                    table-id: 254
                    advmss: 1460

4. List any affected packages or components.
configure-ovs 

openshift-ovn