Description of problem:

After buildah moved from host to private network namespace we faced bug[1] because mtu on `cni-podman0` bridge was higher the local interface.
In bug[1] we were told to set correct mtu in the config file, We were able to solve that issue after setting mtu in  /etc/cni/net.d/87-podman-bridge.conflist.

Now, With netavark introduction we are again facing same issue during container image build(reported in bug[2]) - mtu on `podman0` bridge is higher than interface.

~~~
$ ip link | grep mtu
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN mode DEFAULT group default qlen 1000
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1450 qdisc fq_codel state UP mode DEFAULT group default qlen 1000
3: ovs-system: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN mode DEFAULT group default qlen 1000
4: br-ex: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1350 qdisc noqueue state UNKNOWN mode DEFAULT group default qlen 1000
11: podman0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP mode DEFAULT group default qlen 1000
12: veth49b24621@if2: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue master podman0 state UP mode DEFAULT group default qlen 1000
~~~

Need help with the below queries:-

* Which is default and recommended - netavark or CNI in RHEL9.0?
* How to set mtu in netavark case - Which configuration file(for cni case we were setting mtu in  /etc/cni/net.d/87-podman-bridge.conflist)?


[1] https://bugzilla.redhat.com/show_bug.cgi?id=2060932
[2] https://bugzilla.redhat.com/show_bug.cgi?id=2091816

Version-Release number of selected component (if applicable):

RHEL-9

Version of podman/buildah and netavark:-
~~~
podman-catatonit-4.0.2-7.el9_0.x86_64
podman-4.0.2-7.el9_0.x86_64
buildah-1.24.2-4.el9_0.x86_64
netavark-1.0.1-34.el9_0.x86_64
~~~


How reproducible:

Everytime


Steps to Reproduce:
1) Run an instance in Openstack environment where mtu on interface is set lower than 1500. (It was 1450 in our case)
2) Build container using buildah and try Pull content from outside / Ping outside network with mtu 1500

Actual results:

* dnf install during image build is failing with timeout - Unable to curl the repo metadata:-
~~~  
masked-repo                         2.7 kB/s | 365 kB     02:16    
Errors during downloading metadata for repository 'masked-repo':
  - Curl error (28): Timeout was reached for <url masked for sanity> [Operation too slow. Less than 1000 bytes/sec transferred the last 30 seconds]
~~~

Expected results:

Image build to pass


Additional info:


If we change to cni and set correct mtu in 87-podman-bridge.conflist - things works.

# diff /usr/share/containers/containers.conf /usr/share/containers/containers.conf.backup 
265c265
< network_backend = "cni"
---
> #network_backend = ""


/etc/cni/net.d/87-podman-bridge.conflist
~~~
"mtu": 1450
~~~