[IPSEC]: Fix state modifications in xfrm_state_update().

doing a mod_timer on a live state without holding a lock or for that
matter not even checking whether the state is dead is definitely a bad
idea

net/xfrm/xfrm_state.c

@@ -489,15 +489,16 @@ int xfrm_state_update(struct xfrm_state *x)
 			memcpy(x1->encap, x->encap, sizeof(*x1->encap));
 		memcpy(&x1->lft, &x->lft, sizeof(x1->lft));
 		x1->km.dying = 0;
-		err = 0;
-	}
-	spin_unlock_bh(&x1->lock);
 
 		if (!mod_timer(&x1->timer, jiffies + HZ))
 			xfrm_state_hold(x1);
 		if (x1->curlft.use_time)
 			xfrm_state_check_expire(x1);
 
+		err = 0;
+	}
+	spin_unlock_bh(&x1->lock);
+
 	xfrm_state_put(x1);
 
 	return err;