Merge branch 'net-add-helper-support-in-tc-act_ct-for-ovs-offloading'

Xin Long says:

====================
net: add helper support in tc act_ct for ovs offloading

Ilya reported an issue that FTP traffic would be broken when the OVS flow
with ct(commit,alg=ftp) installed in the OVS kernel module, and it was
caused by that TC didn't support the ftp helper offloaded from OVS.

This patchset is to add the helper support in act_ct for OVS offloading
in kernel net/sched.

The 1st and 2nd patches move some common code into nf_conntrack_helper from
openvswitch so that they could be used by net/sched in the 4th patch (Note
there are still some other common code used in both OVS and TC, and I will
extract it in other patches). The 3rd patch extracts another function in
net/sched to make the 4th patch easier to write. The 4th patch adds this
feature in net/sched.

The user space part will be added in another patch, and with it these OVS
flows (FTP over SNAT) can be used to test this feature:

  table=0, in_port=veth1,tcp,tcp_dst=2121,ct_state=-trk \
    actions=ct(table=1, nat), normal
  table=0, in_port=veth2,tcp,ct_state=-trk actions=ct(table=1, nat)
  table=0, in_port=veth1,tcp,ct_state=-trk actions=ct(table=0, nat)
  table=0, in_port=veth1,tcp,ct_state=+trk+rel actions=ct(commit, nat),normal
  table=0, in_port=veth1,tcp,ct_state=+trk+est actions=veth2"

  table=1, in_port=veth1,tcp,tcp_dst=2121,ct_state=+trk+new \
    actions=ct(commit, nat(src=7.7.16.1), alg=ftp),normal"
  table=1, in_port=veth1,tcp,tcp_dst=2121,ct_state=+trk+est actions=veth2"
  table=1, in_port=veth2,tcp,ct_state=+trk+est actions=veth1"

====================

Link: https://lore.kernel.org/r/cover.1667766782.git.lucien.xin@gmail.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>