[NET]: NETFILTER: remove duplicated lines and fix order in skb_clone().

Some of netfilter-related members are initalized / copied twice in
skb_clone(). Remove one.

Pointed out by Olivier MATZ <olivier.matz@6wind.com>.

And this patch also fixes order of copying / clearing members.

Signed-off-by: YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
Signed-off-by: David S. Miller <davem@davemloft.net>