libbpf: add bpf_object__load_xattr() API function to pass log_level

libbpf was recently made aware of the log_level attribute for programs,
used to specify the level of information expected to be dumped by the
verifier. Function bpf_prog_load_xattr() got support for this log_level
parameter.

But some applications using libbpf rely on another function to load
programs, bpf_object__load(), which does accept any parameter for log
level. Create an API function based on bpf_object__load(), but accepting
an "attr" object as a parameter. Then add a log_level field to that
object, so that applications calling the new bpf_object__load_xattr()
can pick the desired log level.

v3:
- Rewrite commit log.

v2:
- We are in a new cycle, bump libbpf extraversion number.

Signed-off-by: Quentin Monnet <quentin.monnet@netronome.com>
Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

src/libbpf.map

@@ -171,4 +171,5 @@ LIBBPF_0.0.4 {
 		btf_dump__free;
 		btf_dump__new;
 		btf__parse_elf;
+		bpf_object__load_xattr;
 } LIBBPF_0.0.3;