Merge branch 'bpf: mptcp: Support for mptcp_sock'

Mat Martineau says:

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

This patch set adds BPF access to mptcp_sock structures, along with
associated self tests. You may recognize some of the code from earlier
(https://lore.kernel.org/bpf/20200918121046.190240-6-nicolas.rybowski@tessares.net/)
but it has been reworked quite a bit.

v1 -> v2: Emit BTF type, add func_id checks in verifier.c and bpf_trace.c,
remove build check for CONFIG_BPF_JIT, add selftest check for CONFIG_MPTCP,
and add a patch to include CONFIG_IKCONFIG/CONFIG_IKCONFIG_PROC for the
BPF self tests.

v2 -> v3: Access sysctl through the filesystem to work around CI use of
the more limited busybox sysctl command.

v3 -> v4: Dropped special case kernel code for tcp_sock is_mptcp, use
existing bpf_tcp_helpers.h, and add check for 'ip mptcp monitor' support.

v4 -> v5: Use BPF test skeleton, more consistent use of ASSERT macros,
drop some unnecessary parameters / checks, and use tracing to acquire
MPTCP token.

Geliang Tang (6):
  bpf: add bpf_skc_to_mptcp_sock_proto
  selftests/bpf: Enable CONFIG_IKCONFIG_PROC in config
  selftests/bpf: test bpf_skc_to_mptcp_sock
  selftests/bpf: verify token of struct mptcp_sock
  selftests/bpf: verify ca_name of struct mptcp_sock
  selftests/bpf: verify first of struct mptcp_sock
====================

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>