My home router doesn't handle IPv6, and for that matter, neither does my ISP, so I get a lot of IPv6 related garbage in my syslog and kern.log. To turn it off, you need to create a new file, rather than editing a system file, and then reload these settings.
sudo nano /etc/sysctl.d/95-disable-ipv6.conf
#add the following lines
net.ipv6.conf.all.disable_ipv6 = 1
net.ipv6.conf.default.disable_ipv6 = 1
net.ipv6.conf.lo.disable_ipv6 = 1
# reload kernel parameters
sudo service procps reload
# Check that its taken ... the result of this should be 1
cat /proc/sys/net/ipv6/conf/all/disable_ipv6
Nice.