Merge branch 'Various BPF helper improvements'

Daniel Borkmann says:

====================
This series adds two BPF helpers, that is, one for retrieving the classid
of an skb and another one to redirect via the neigh subsystem, and improves
also the cookie helpers by removing the atomic counter. I've also added
the bpf_tail_call_static() helper to the libbpf API that we've been using
in Cilium for a while now, and last but not least the series adds a few
selftests. For details, please check individual patches, thanks!

v3 -> v4:
  - Removed out_rec error path (Martin)
  - Integrate BPF_F_NEIGH flag into rejecting invalid flags (Martin)
    - I think this way it's better to avoid bit overlaps given it's
      right in the place that would need to be extended on new flags
v2 -> v3:
  - Removed double skb->dev = dev assignment (David)
  - Added headroom check for v6 path (David)
  - Set set flowi4_proto for ip_route_output_flow (David)
  - Rebased onto latest bpf-next
v1 -> v2:
  - Rework cookie generator to support nested contexts (Eric)
  - Use ip_neigh_gw6() and container_of() (David)
  - Rename __throw_build_bug() and improve comments (Andrii)
  - Use bpf_tail_call_static() also in BPF samples (Maciej)
====================

Signed-off-by: Alexei Starovoitov <ast@kernel.org>