Merge branch 'bpftool-improvements'

Martin Lau says:

====================
When a map is storing a kernel's struct, its
map_info->btf_vmlinux_value_type_id is set.  The first map type
supporting it is BPF_MAP_TYPE_STRUCT_OPS.

This series adds support to dump this kind of map with BTF.
The first two patches are bug fixes which are only applicable to
bpf-next.

Please see individual patches for details.

v3:
- Remove unnecessary #include "libbpf_internal.h" from patch 5

v2:
- Expose bpf_find_kernel_btf() as a LIBBPF_API in patch 3 (Andrii)
- Cache btf_vmlinux in bpftool/map.c (Andrii)
====================

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