Merge branch 'selftests/bpf: BTF-based kernel data display'

Alan Maguire says:

====================
Resolve issues in bpf selftests introduced with BTF-based kernel data
display selftests; these are

- a warning introduced in snprintf_btf.c; and
- compilation failures with old kernels vmlinux.h
====================

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