sched: add new attr TCA_EXT_WARN_MSG to report tc extact message

We will report extack message if there is an error via netlink_ack(). But if the rule is not to be exclusively executed by the hardware, extack is not passed along and offloading failures don't get logged. In commit 81c7288b170a ("sched: cls: enable verbose logging") Marcelo made cls could log verbose info for offloading failures, which helps improving Open vSwitch debuggability when using flower offloading. It would also be helpful if userspace monitor tools, like "tc monitor", could log this kind of message, as it doesn't require vswitchd log level adjusment. Let's add a new tc attributes to report the extack message so the monitor program could receive the failures. e.g. # tc monitor added chain dev enp3s0f1np1 parent ffff: chain 0 added filter dev enp3s0f1np1 ingress protocol all pref 49152 flower chain 0 handle 0x1 ct_state +trk+new not_in_hw action order 1: gact action drop random type none pass val 0 index 1 ref 1 bind 1 Warning: mlx5_core: matching on ct_state +new isn't supported. In this patch I only report the extack message on add/del operations. It doesn't look like we need to report the extack message on get/dump operations. Note this message not only reporte to multicast groups, it could also be reported unicast, which may affect the current usersapce tool's behaivor.

HLHangbin Liu committed 3 years ago