bpf: tcp: Add bpf_cubic example

This set adds bpf_cubic.c example.  It was separated from the
earlier BPF STRUCT_OPS series.  Some highlights since the
last post:

1. It is based on EricD recent fixes to the kernel tcp_cubic. [1]
2. The bpf jiffies reading helper is inlined by the verifier.
   Different from the earlier version, it only reads jiffies alone
   and does not do usecs/jiffies conversion.
3. The bpf .kconfig map is used to read CONFIG_HZ.

[1]: https://patchwork.ozlabs.org/cover/1215066/

v3:
- Remove __weak from CONFIG_HZ in patch 3. (Andrii)

v2:
- Move inlining to fixup_bpf_calls() in patch 1. (Daniel)
- It is inlined for 64 BITS_PER_LONG and jit_requested
  as the map_gen_lookup().  Other cases could be
  considered together with map_gen_lookup() if needed.
- Use usec resolution in bictcp_update() calculation in patch 3.
  usecs_to_jiffies() is then removed().  (Eric)

Martin KaFai Lau (3):
  bpf: Add BPF_FUNC_jiffies64
  bpf: Sync uapi bpf.h to tools/
  bpf: tcp: Add bpf_cubic example

 include/linux/bpf.h                           |   1 +
 include/uapi/linux/bpf.h                      |   9 +-
 kernel/bpf/core.c                             |   1 +
 kernel/bpf/helpers.c                          |  12 +
 kernel/bpf/verifier.c                         |  24 +
 net/core/filter.c                             |   2 +
 tools/include/uapi/linux/bpf.h                |   9 +-
 tools/testing/selftests/bpf/bpf_tcp_helpers.h |  16 +
 .../selftests/bpf/prog_tests/bpf_tcp_ca.c     |  25 +
 tools/testing/selftests/bpf/progs/bpf_cubic.c | 544 ++++++++++++++++++
 10 files changed, 641 insertions(+), 2 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/progs/bpf_cubic.c

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2.17.1