libbpf: Don't enforce unnecessary verifier log restrictions on libbpf side

This basically prevents any forward compatibility. And we either way
just return -EINVAL, which would otherwise be returned from bpf()
syscall anyways.

Similarly, drop enforcement of non-NULL log_buf when log_level > 0. This
won't be true anymore soon.
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Lorenz Bauer <lmb@isovalent.com>
Link: https://lore.kernel.org/bpf/20230406234205.323208-5-andrii@kernel.org

tools/lib/bpf/bpf.c

@@ -290,10 +290,6 @@ int bpf_prog_load(enum bpf_prog_type prog_type,
 
 	if (!!log_buf != !!log_size)
 		return libbpf_err(-EINVAL);
-	if (log_level > (4 | 2 | 1))
-		return libbpf_err(-EINVAL);
-	if (log_level && !log_buf)
-		return libbpf_err(-EINVAL);
 
 	func_info_rec_size = OPTS_GET(opts, func_info_rec_size, 0);
 	func_info = OPTS_GET(opts, func_info, NULL);