Hostname getting set to fqdn after upgrading to cloud-init-22.2

Hi All,

Environment details:
cloud-init-22.2
Photon OS 3.0 and above

I am seeing something weird after upgrading to cloud-init-22.2

My /etc/hosts looks like this:

$ cat /etc/hosts
127.0.1.1 ph3dev.local ph3dev
127.0.0.1 localhost

And my /etc/hostname

$ cat /etc/hostname
ph3dev

Now if I do systemctl restart cloud-init , /etc/hostname is getting changed.

$ cat /etc/hostname
ph3dev.local

And hostname command return fqdn instead of short name. Isn't it incorrect to have fqdn in /etc/hostname?

I have prefer_fqdn_over_hostname = True in photon.py

I changed frequency = PER_ONCE in cc_set_hostname.py and it doesn't modify /etc/hostname after that and this is how it was in cloud-init <= v22.1 and even in v22.1 we have prefer_fqdn_over_hostname set in photon.py but it doesn't modify /etc/hostname file.

I doubt that https://github.com/canonical/cloud-init/pull/1365 has introduced this change, not sure though.

We discussed a bit about this issue in https://github.com/canonical/cloud-init/pull/1365.

If it helps, I see the follwing entries in cloud-init-22.1 logs:

```
2022-08-08 06:58:38,498 - stages.py[DEBUG]: Running module set_hostname (<module 'cloudinit.config.cc_set_hostname' from '/usr/lib/python3.7/site-packages/cloudinit/config/cc_set_hostname.py'>) with frequency once-per-instance
```

And in cloud-init-22.2:
```
2022-08-08 07:00:38,512 - modules.py[DEBUG]: Running module set_hostname (<module 'cloudinit.config.cc_set_hostname' from '/usr/lib/python3.7/site-packages/cloudinit/config/cc_set_hostname.py'>) with frequency always
```
```