[docker-fpm-frr] Change the ownership of files within /etc/frr/ to frr

[shikenghua]

- What I did
The owner of the files generated by start.sh (/etc/frr/*.conf) is root if it is a new file. This will cause error when executing "copy running-config startup-config" in vtysh because of privilege issue. The owner of all conf files within /etc/frr/ need to be changed to frr.
Note: The "RUN chown -R ${frr_user_uid}:${frr_user_gid} /etc/frr/" command in Dockerfile only works on existing files.

- How I did it
Add "chown -R frr:frr /etc/frr/" in start.sh

- How to verify it
Test with "copy running-config startup-config" command in vtysh.

- Description for the changelog

- A picture of a cute animal (not mandatory but encouraged)

[mikelazar]

This is really useful - otherwise changes made with "write mem" from vtysh cannot be saved.

Would it be possible to merge this pull request soon ?

[shikenghua]

This is really useful - otherwise changes made with "write mem" from vtysh cannot be saved.

Would it be possible to merge this pull request soon ?

I have no idea. It is a very simple change and the pull request was submitted 6 weeks ago but no one review it yet. Maybe just wait...