Set TFTP file permissions to 0644

The TFTP server used by ironic and ironic inspector (in.tftpd) requires
files to be world readable in order for them to be accessible via
TFTP[1].

The permissions of these files were recently changed to 0600 along with
a number of other files[2].

This change reverts the permissions to 0644 for the ironic inspector PXE
configuration files.

[1] https://linux.die.net/man/8/in.tftpd (security section)
[2]
https://github.com/openstack/kolla-ansible/commit/274291463e99eab805a4265adc856c1bffafa9ad

Change-Id: Ibc281949ebf5bab1e1d2e450ec943728aa00943b
Closes-Bug: #1701695

ansible/roles/ironic/templates/ironic-pxe.json.j2

@@ -6,20 +6,20 @@
             "source": "{{ container_config_directory }}/ironic-agent.kernel",
             "dest": "/tftpboot/ironic-agent.kernel",
             "owner": "root",
-            "perm": "0600"
+            "perm": "0644"
         },
         {
             "source": "{{ container_config_directory }}/ironic-agent.initramfs",
             "dest": "/tftpboot/ironic-agent.initramfs",
             "owner": "root",
-            "perm": "0600"
+            "perm": "0644"
         },
 {% endif %}
         {
             "source": "{{ container_config_directory }}/default",
             "dest": "/tftpboot/pxelinux.cfg/default",
             "owner": "root",
-            "perm": "0600"
+            "perm": "0644"
         }
     ],
     "permissions": [