libbpf: use explicit map reuse flag to skip map creation steps

Instead of inferring whether map already point to previously
created/pinned BPF map (which user can specify with bpf_map__reuse_fd()) API),
use explicit map->reused flag that is set in such case.
Acked-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20240104013847.3875810-3-andrii@kernel.orgSigned-off-by: Alexei Starovoitov <ast@kernel.org>

tools/lib/bpf/libbpf.c

@@ -5465,7 +5465,7 @@ bpf_object__create_maps(struct bpf_object *obj)
 			}
 		}
 
-		if (map->fd >= 0) {
+		if (map->reused) {
 			pr_debug("map '%s': skipping creation (preset fd=%d)\n",
 				 map->name, map->fd);
 		} else {