Description of problem:
during the procedure to change mtu from  Red Hat doc , machineconfig in the step 2 of the procedure applied but didn't update the MTU on primary network interface as expected.

Version-Release number of selected component (if applicable): OCP4.18, OCP 4.16, OCP 4.14

How reproducible:
it's systematic 

Steps to Reproduce:

1. apply step 1 of change MTU procedure from RH official doc (the goal is to update machineNetwork MTU from 9000 to 9100)
  

oc patch Network.operator.openshift.io cluster --type=merge --patch \
  '{"spec": { "migration": { "mtu": { "network": { "from": 8900, "to": 8900 } , "machine": { "to" : 9100 } } } } }' 

2. Apply step 2 of the official doc:  machineconfig to create a config file /etc/NetworkManager/conf.d/<interface>-mtu.conf  to update primary network mtu 

3. Verify if MTU is update on primary network interface 

Actual results:
MTU is not updated on primary network interface as MTU was already set for this interface  in  /etc/NetworkManager/system-connections/<interface>.nmconnection during cluster/deployment using ZTP/GitOps

Expected results:
MTU to be update on primary network interface 

Additional info:

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Affected Platforms: Baremetal OVN-Kubernetes - OCP 4.18 , OCP 4.16

Is it an

1. customer issue / SD
2. internal RedHat testing failure

We have a setup you can provide access to reproduce the issue and tested the propose solution.