We need to return EOPNOTSUPP for the unsupported mpls action type when
setup the flow action.

In the original implement, we will return 0 for the unsupported mpls
action type, actually we do not setup it and the following actions
to the flow action entry.

Fixes: 9838b20a ("net: sched: take rtnl lock in tc_setup_flow_action()")
Signed-off-by: Baowen Zheng <baowen.zheng@corigine.com>
Signed-off-by: Simon Horman <simon.horman@corigine.com>
Acked-by: Jamal Hadi Salim <jhs@mojatatu.com>
Signed-off-by: David S. Miller <davem@davemloft.net>