I thought there is something wrong with my config, it turned out that the Casper NetSUS cannot config well with CentOS.
modify /lib/systemd/system/tftp.service
ExecStart=/usr/sbin/in.tftpd -s /srv/NetBoot/NetBootSP0and then:
setsebool -P tftp_anon_write 1
setsebool -P tftp_home_dir 1
when you check, they are all on now. then I did a reboot :
getsebool -a | grep tftp
Links to read:
https://github.com/jamf/NetSUS/issues/74
https://www.jamf.com/jamf-nation/discussions/21033/netsus-on-centos-7