In clip_mkip(), skb->dev is dereferenced after clip_push(),
which frees up skb.

Advisory: AD_LAB-06009 (<adlab@venustech.com.cn>).
Signed-off-by: NYOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>