iptables: move ip6tables-extra to IPv6 menu

Signed-off-by: Claudio Leite <leitec@staticky.com>
kernel: add experimental zram swap support

Backported from trunk. Not guaranteed for anything at the
moment, i.e. it might be terrible and unstable.

Signed-off-by: Claudio Leite <leitec@staticky.com>