libbpf: Mark bpf_object__open_buffer() API deprecated

Deprecate bpf_object__open_buffer() API in favor of the unified
opts-based bpf_object__open_mem() API.
Signed-off-by: Christy Lee <christylee@fb.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20220125005923.418339-2-christylee@fb.com

tools/lib/bpf/libbpf.h

@@ -180,6 +180,7 @@ bpf_object__open_mem(const void *obj_buf, size_t obj_buf_sz,
 		     const struct bpf_object_open_opts *opts);
 
 /* deprecated bpf_object__open variants */
+LIBBPF_DEPRECATED_SINCE(0, 8, "use bpf_object__open_mem() instead")
 LIBBPF_API struct bpf_object *
 bpf_object__open_buffer(const void *obj_buf, size_t obj_buf_sz,
 			const char *name);