Merge branch 'bpf-flow-dissector-fixes'

Stanislav Fomichev says:

====================
This patch series fixes the existing BPF flow dissector API to
support calling BPF progs from the eth_get_headlen context (the
support itself will be added in bpf-next tree).

The summary of the changes:

  * fix VLAN handling in bpf_flow.c, we don't need to peek back and look
    at skb->vlan_present; add selftests
  * pass and use flow_keys->n_proto instead of skb->protocol
  * fix clamping of flow_keys->nhoff for packets with nhoff > 0
  * prohibit access to most of the __sk_buff fields from BPF flow
    dissector progs; only data/data_end/flow_keys are allowed (all input
    is now passed via flow_keys)
  * finally, document BPF flow dissector program environment
====================

Acked-by: Willem de Bruijn <willemb@google.com>
Acked-by: Petar Penkov <peterpenkov96@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>