ipv6: ndisc: fix ndisc_send_redirect writing to the wrong skb

Since some refactoring in 5f5a011, ndisc_send_redirect called
ndisc_fill_redirect_hdr_option on the wrong skb, leading to data corruption or
in the worst case a panic when the skb_put failed.

Signed-off-by: Matthias Schiffer <mschiffer@universe-factory.net>
Reviewed-by: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>