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]
274291463e
Change-Id: Ibc281949ebf5bab1e1d2e450ec943728aa00943b
Closes-Bug: #1701695
e50f19522a