Merge branch 'bpf-tests-probe-kernel-support'

Stanislav Fomichev says:

====================
If test_maps/test_verifier is running against the kernel which doesn't
have _all_ BPF features enabled, it fails with an error. This patch
series tries to probe kernel support for each failed test and skip
it instead. This lets users run BPF selftests in the not-all-bpf-yes
environments and received correct PASS/NON-PASS result.

See https://www.spinics.net/lists/netdev/msg539331.html for more
context.

The series goes like this:

* patch #1 skips sockmap tests in test_maps.c if BPF_MAP_TYPE_SOCKMAP
  map is not supported (if bpf_create_map fails, we probe the kernel
  for support)
* patch #2 skips verifier tests if test->prog_type is not supported (if
  bpf_verify_program fails, we probe the kernel for support)
* patch #3 skips verifier tests if test fixup map is not supported (if
  create_map fails, we probe the kernel for support)
* next patches fix various small issues that arise from the first four:
  * patch #4 sets "unknown func bpf_trace_printk#6" prog_type to
    BPF_PROG_TYPE_TRACEPOINT so it is correctly skipped in
    CONFIG_BPF_EVENTS=n case
  * patch #5 exposes BPF_PROG_TYPE_CGROUP_{SKB,SOCK,SOCK_ADDR} only when
    CONFIG_CGROUP_BPF=y, this makes verifier correctly skip appropriate
    tests

v3 changes:
* rebased on top of Quentin's series which adds probes to libbpf

v2 changes:
* don't sprinkle "ifdef CONFIG_CGROUP_BPF" all around net/core/filter.c,
  doing it only in the bpf_types.h is enough to disable
  BPF_PROG_TYPE_CGROUP_{SKB,SOCK,SOCK_ADDR} prog types for non-cgroup
  enabled kernels
====================

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>