reload_all() {
  /sbin/shorewall restart
echo "Starting ez-ipupd from dhclient ..."
  /etc/init.d/ez-ipupd start

}

All you need is to add the command /etc/init.d/ez-ipupd -start to /etc/ppp/ip-up.

# Main Script starts here
#
/etc/init.d/ez-ipupd start

run-parts /etc/ppp/ip-up.d
[ -x /bin/beep ] && /bin/beep -f 600 -n -f 900 -n -f1200 -n -f1800
# last line

You need to add a rule to allow accessing port 80 from your firewall on the net zone. To make ez-ipupdate work. There for add to /etc/shorewall/rules

ACCEPT         fw       net           tcp      80