extensions: libxt_socket: update man page

Document --nowildcard option and its implications when using -m socket
to intercept packets.

While at it, update man page with Balazs Scheidlers comments from
nf_tproxy_core.h in kernel tree to better explain how lookup is performed.

Cc: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: Florian Westphal <fw@strlen.de>
doc: add libnetfilter_queue pointer to libxt_NFQUEUE.man

... and remove the QUEUE snippets from ip(6)tables man page,
the queue target was replaced by nfqueue years ago.
Fix up a couple of needless differences in ip(6)tables.8, too.

Signed-off-by: Florian Westphal <fw@strlen.de>
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>