I got the following configuration:
server:/srv/tftpboot # grep dnsmasq.d /etc/dnsmasq.conf
conf-dir=/etc/dnsmasq.d

and in /etc/dnsmasq.d/tftp:
/etc/dnsmasq.d/tftp:enable-tftp
/etc/dnsmasq.d/tftp:tftp-root=/srv/tftpboot

This causes dnsmasq to refuse restart after every update:

20170528-10:31:44.9 systemd[1]: Starting DNS caching server....
20170528-10:31:44.9 dnsmasq[21075]: dnsmasq: syntax check OK.
20170528-10:31:44.9 systemd[1]: Started DNS caching server..
20170528-10:31:44.9 dnsmasq[21079]: TFTP directory /srv/tftpboot inaccessible:
Permission denied
20170528-10:31:44.9 systemd[1]: dnsmasq.service: Main process exited,
code=exited, status=3/NOTIMPLEMENTED
20170528-10:31:44.9 dnsmasq[21079]: FAILED to start up
20170528-10:31:44.9 systemd[1]: dnsmasq.service: Unit entered failed state.
20170528-10:31:44.9 systemd[1]: dnsmasq.service: Failed with result
'exit-code'.
20170528-10:32:49.6 systemd[1]: Stopped DNS caching server..

The reason is this:

server:/srv/tftpboot # rpm -qlv dnsmasq |grep tftpboot
drwxr-x---    2 tftp    tftp                        0 Mai 16 12:06
/srv/tftpboot

Even though dnsmasq user is in group tftp:
server:/srv/tftpboot # id dnsmasq
uid=106(dnsmasq) gid=116(tftp) groups=116(tftp)

this seems to be not enough.
After every update I have to chmod 755 /srv/tftpboot to get dnsmasq starting up
again.