libbpf: Adjust SEC short cut for expected attach type BPF_XDP_DEVMAP

Adjust the SEC("xdp_devmap/") prog type prefix to contain a
slash "/" for expected attach type BPF_XDP_DEVMAP.  This is consistent
with other prog types like tracing.

Fixes: 27787970 ("libbpf: Add SEC name for xdp programs attached to device map")
Suggested-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Link: https://lore.kernel.org/bpf/159309521882.821855.6873145686353617509.stgit@firesoul

tools/lib/bpf/libbpf.c

@@ -6659,7 +6659,7 @@ static const struct bpf_sec_def section_defs[] = {
 		.expected_attach_type = BPF_TRACE_ITER,
 		.is_attach_btf = true,
 		.attach_fn = attach_iter),
-	BPF_EAPROG_SEC("xdp_devmap",		BPF_PROG_TYPE_XDP,
+	BPF_EAPROG_SEC("xdp_devmap/",		BPF_PROG_TYPE_XDP,
 						BPF_XDP_DEVMAP),
 	BPF_PROG_SEC("xdp",			BPF_PROG_TYPE_XDP),
 	BPF_PROG_SEC("perf_event",		BPF_PROG_TYPE_PERF_EVENT),

tools/testing/selftests/bpf/progs/test_xdp_with_devmap_helpers.c

@@ -27,7 +27,7 @@ int xdp_dummy_prog(struct xdp_md *ctx)
 /* valid program on DEVMAP entry via SEC name;
  * has access to egress and ingress ifindex
  */
-SEC("xdp_devmap")
+SEC("xdp_devmap/map_prog")
 int xdp_dummy_dm(struct xdp_md *ctx)
 {
 	char fmt[] = "devmap redirect: dev %u -> dev %u len %u\n";