gossipd: annotate replace_broadcast that we take() the payload, make it const.

We tal_dup_arr() it, which does take.  Make it const in the structure;
the tal_dup_arr() removes the const, so it compiles without it, but it's
misleading.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

gossipd/broadcast.c

@@ -18,7 +18,7 @@ static void destroy_queued_message(struct queued_message *msg,
 
 static struct queued_message *new_queued_message(const tal_t *ctx,
 						 struct broadcast_state *bstate,
-						 const u8 *payload,
+						 const u8 *payload TAKES,
 						 u64 index)
 {
 	struct queued_message *msg = tal(ctx, struct queued_message);
@@ -32,7 +32,7 @@ static struct queued_message *new_queued_message(const tal_t *ctx,
 bool replace_broadcast(const tal_t *ctx,
 		       struct broadcast_state *bstate,
 		       u64 *index,
-		       const u8 *payload)
+		       const u8 *payload TAKES)
 {
 	struct queued_message *msg;
 	bool evicted = false;

gossipd/broadcast.h

@@ -14,7 +14,7 @@ struct queued_message {
 	u64 index;
 
 	/* Serialized payload */
-	u8 *payload;
+	const u8 *payload;
 };
 
 struct broadcast_state {
@@ -31,7 +31,7 @@ struct broadcast_state *new_broadcast_state(tal_t *ctx);
 bool replace_broadcast(const tal_t *ctx,
 		       struct broadcast_state *bstate,
 		       u64 *index,
-		       const u8 *payload);
+		       const u8 *payload TAKES);
 
 
 struct queued_message *next_broadcast_message(struct broadcast_state *bstate, u64 last_index);