I'm not a fan of IPv6, so I disable it wherever I can. The number of devices in my network is still manageable with IPv4...
You have to edit /etc/default/grub:
sudo nano /etc/default/grub... and insert / edit the following lines
GRUB_CMDLINE_LINUX_DEFAULT="ipv6.disable=1 quiet splash"
GRUB_CMDLINE_LINUX="ipv6.disable=1"Afterwards execute:
sudo update-grub... and reboot your PC