TC: refactor act_mirred packets re-injection

This series is aimed at improving the act_mirred redirect performances. Such action is used by OVS to represent TC S/W flows, and it's current largest bottle-neck is the need for a skb_clone() for each packet.

The first 2 patches introduce some cleanup and safeguards to allow extending tca_result - we will use it to store RCU protected redirect information - and introduce a clear separation between user-space accessible tcfa_action values and internal values accessible only by the kernel.
Then a new tcfa_action value is introduced: TC_ACT_REINJECT, similar to TC_ACT_REDIRECT, but preserving the mirred semantic. Such value is not accessible from user-space.
The last patch exploits the newly introduced infrastructure in the act_mirred action, to avoid a skb_clone, when possible.

Overall this the above gives a ~10% performance improvement in forwarding tput, when using the TC S/W datapath.

v1 -> v2:
- preserve the rcu lock in act_bpf
- add and use a new action value to reinject the packets, preserving the mirred semantic

v2 -> v3:
- renamed to new action as TC_ACT_REINJECT
- TC_ACT_REINJECT is not exposed to user-space

v3 -> v4:
- dropped the TC_ACT_REDIRECT patch
- report failure via extack, too
- rename the new action as TC_ACT_REINSERT
- skip clone only if the control action don't touch tcf_result

v4 -> v5:
- fix a couple of build issue reported by kbuild bot
- dont split messages

Paolo Abeni (4):
net/sched: user-space can't set unknown tcfa_action values tc/act: remove unneeded RCU lock in action callback net/tc: introduce TC_ACT_REINSERT.
act_mirred: use TC_ACT_REINSERT when possible

 include/net/act_api.h        |  2 +-
 include/net/pkt_cls.h        |  3 ++
 include/net/sch_generic.h    | 30 +++++++++++++++++++
 include/uapi/linux/pkt_cls.h |  6 ++--
 net/core/dev.c               |  6 +++-
 net/sched/act_api.c          | 14 +++++++++
 net/sched/act_csum.c         | 12 ++------
 net/sched/act_ife.c          |  5 +---
 net/sched/act_mirred.c       | 57 ++++++++++++++++++++++++++++--------
 net/sched/act_sample.c       |  4 +--
 net/sched/act_skbedit.c      | 10 ++-----
 net/sched/act_skbmod.c       | 21 ++++++-------
 net/sched/act_tunnel_key.c   |  6 +---
 net/sched/act_vlan.c         | 19 +++++-------
 14 files changed, 126 insertions(+), 69 deletions(-)

2.17.1