doc: merge ip6table man pages into ipv4 ones

a couple of improvements to the iptables man page never made it into
ip6tables version.

The number of differences between these two files is so small that
it seems preferable to alias the ipv6 man pages to their ipv4 counterpart
and change iptables man page to specifically document differences
(e.g. lack of ip6tables -f, etc).

Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
10 files changed