[XFRM] Call dst_check() with appropriate cookie

This fixes infinite loop issue with IPv6 tunnel mode.
Signed-off-by: NKazunori Miyazawa <kazunori@miyazawa.org>
Signed-off-by: NHideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>