Changing the order of checks in entrypoint 10

[aqeelat]

Wouldn't flipping these lines make more sense?
If ipv6 is enabled then we wouldn't need to check if the file is writable. The exit message will be more informative, instead of sending the user in a wild hunt.

https://github.com/nginxinc/docker-nginx/blob/6a4c0cb4ac7e53bbbe473df71b61a5bf9f95252f/entrypoint/10-listen-on-ipv6-by-default.sh#L26-L30