The reason why your kernel parameter settings are not working and cause an error during boot about unknown key is that
ipv6 module is not yet loaded. To get it loaded before these keys are set, do as root:
echo "ipv6" >> /etc/modules
The kernel parameters can be set to /etc/sysctl.conf or alternatively create a file into /etc/sysctl.d/disableipv6.conf and add the key there, for example:
echo "net.ipv6.conf.all.disable_ipv6=1" > /etc/sysctl.d/disableipv6.conf
To see if it worked:
sysctl -a |grep disable_ipv6