net: dsa: felix: Annotate struct action_gate_entry with __counted_by

Add the __counted_by compiler attribute to the flexible array member
entries to improve access bounds-checking via CONFIG_UBSAN_BOUNDS and
CONFIG_FORTIFY_SOURCE.

Signed-off-by: Hongbo Li <lihongbo22@huawei.com>
Link: https://patch.msgid.link/20240904014956.2035117-1-lihongbo22@huawei.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

drivers/net/dsa/ocelot/felix_vsc9959.c

@@ -1733,7 +1733,7 @@ struct felix_stream_gate {
 	u64 cycletime;
 	u64 cycletime_ext;
 	u32 num_entries;
-	struct action_gate_entry entries[];
+	struct action_gate_entry entries[] __counted_by(num_entries);
 };
 
 struct felix_stream_gate_entry {