[XFRM]: Avoid bogus BUG() when throwing new policy away.

From: YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>

When we destory a new policy entry, we need to tell
xfrm_policy_destroy() explicitly that the entry is not
alive yet.
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/xfrm/xfrm_user.c

@@ -1105,6 +1105,7 @@ static struct xfrm_policy *xfrm_policy_construct(struct xfrm_userpolicy_info *p,
 	return xp;
  error:
 	*errp = err;
+	xp->dead = 1;
 	xfrm_policy_destroy(xp);
 	return NULL;
 }