net/ipv6: Refactor address dump to push inet6_fill_args to in6_dump_addrs

Pull the inet6_fill_args arg up to in6_dump_addrs and move netnsid
into it.

Signed-off-by: David Ahern <dsahern@gmail.com>
Acked-by: Christian Brauner <christian@brauner.io>
Signed-off-by: David S. Miller <davem@davemloft.net>