gossip: Moving to intmap-based broadcast for the legacy daemon

Moved the broadcast functionality to broadcast.[ch]. So far this
includes only the enqueuing side of broadcasts, the dequeuing and
actual push to the peer is daemon dependent. This also adds the
broadcast_state to the routing_state and the last broadcast index to
the peer for the legacy daemon.

daemon/broadcast.h

@@ -0,0 +1,43 @@
+#ifndef LIGHTNING_DAEMON_BROADCAST_H
+#define LIGHTNING_DAEMON_BROADCAST_H
+#include "config.h"
+
+#include <ccan/intmap/intmap.h>
+#include <ccan/list/list.h>
+#include <ccan/short_types/short_types.h>
+#include <ccan/tal/tal.h>
+
+/* Common functionality to implement staggered broadcasts with replacement. */
+
+struct queued_message {
+	int type;
+
+	/* Unique tag specifying the msg origin */
+	void *tag;
+
+	/* Timestamp for `channel_update`s and `node_announcement`s, 0
+	 * for `channel_announcement`s */
+	/*u32 timestamp;*/
+
+	/* Serialized payload */
+	u8 *payload;
+
+        //FIXME(cdecker) Remove after migrating to intmap
+	struct list_node list;
+};
+
+struct broadcast_state {
+u32 next_index;
+UINTMAP(struct queued_message *) broadcasts;
+};
+
+struct broadcast_state *new_broadcast_state(tal_t *ctx);
+
+void queue_broadcast(struct broadcast_state *bstate,
+			     const int type,
+			     const u8 *tag,
+			     const u8 *payload);
+
+struct queued_message *next_broadcast_message(struct broadcast_state *bstate, u64 *last_index);
+
+#endif /* LIGHTNING_DAEMON_BROADCAST_H */