To disable ip6, please try:
# check ipv6
ifconfig -a | grep inet6
# make folder for template
mkdir -p /etc/e-smith/templates-custom/etc/sysctl.conf
# create template-file
nano /etc/e-smith/templates-custom/etc/sysctl.conf/99sysctl
# content of 99sysctl
net.ipv6.conf.all.disable_ipv6 = 1
# expand template
expand-template /etc/sysctl.conf
# To reflect the changes
sysctl -p
# check ipv6 again
ifconfig -a | grep inet6