I even change file

/run/overlay/etc.overlay/upper/sysconfig/network/ifcfg-mgmt-br

/run/overlay/etc.overlay/upper/sysconfig/network/ifcfg-mgmt-bo` which looks like this:

TARTMODE='onboot'
BOOTPROTO='static'
BRIDGE='yes'
BRIDGE_STP='off'
BRIDGE_FORWARDDELAY='0'
BRIDGE_PORTS='mgmt-bo'
PRE_UP_SCRIPT="wicked:setup_bridge.sh"
POST_UP_SCRIPT="wicked:setup_bridge.sh"

IPADDR=10.150.2.31
NETMASK=255.255.255.0


DHCLIENT_SET_DEFAULT_ROUTE='yes'

MTU=9000

I changed MTU to 1500 and in

/oem/harvester.config

but after reboot somescript is regenerating

/run/overlay/etc.overlay/upper/sysconfig/network/ifcfg-mgmt-br

and

ifcfg-mgmt-bo

and it’s back to 9000 after reboot.