The package provided by the upstream project already includes 
/etc/init.d/firewalld which will get executed on boot by
/etc/rc.d/rc.sysvinit. So technically, you don't have to 
use the custom rc.firewalld. I have provided a patch that
changes /etc/sysconfig/ to /etc/default in order to source 
any custom arguments.

Otherwise, feel free to chmod -x /etc/init.d/firewalld
and chmod +x /etc/rc.d/rc.firewalld then add it to your
/etc/rc.d/rc.local like so:

if [ -x /etc/rc.d/rc.firewalld ]; then
        /etc/rc.d/rc.firewalld start
fi

and the following to /etc/rc.d/rc.local_shutdown:

if [ -x /etc/rc.d/rc.firewalld ]; then
        /etc/rc.d/rc.firewalld stop
fi