sched: cls_flower: fix panic on filter replace

The following test case causes a NULL pointer dereference in cls_flower:

  tc filter add dev foo parent 1: flower eth_type ipv4 action ok flowid 1:1
  tc filter replace dev foo parent 1: pref 49152 handle 0x1 \
            flower eth_type ipv6 action ok flowid 1:1

The problem is that commit 77b9900e ("tc: introduce Flower classifier")
accidentally swapped the arguments of list_replace_rcu(), the old
element needs to be the first argument and the new element the second.

Fixes: 77b9900e

 ("tc: introduce Flower classifier")
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Jiri Pirko <jiri@resnulli.us>
Signed-off-by: David S. Miller <davem@davemloft.net>