net: sched: update the nat flag for icmp error packets in ct_nat_execute

In ovs_ct_nat_execute(), the packet flow key nat flags are updated
when it processes ICMP(v6) error packets translation successfully.

In ct_nat_execute() when processing ICMP(v6) error packets translation
successfully, it should have done the same in ct_nat_execute() to set
post_ct_s/dnat flag, which will be used to update flow key nat flags
in OVS module later.

Reviewed-by: Saeed Mahameed <saeed@kernel.org>
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>