daemon: handle feechange requests.

I originally overloaded struct htlc for this, as they go through the
same states, but separating them turned out to be clearer.

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

daemon/peer.h

@@ -7,6 +7,7 @@
 #include "bitcoin/script.h"
 #include "bitcoin/shadouble.h"
 #include "channel.h"
+#include "feechange.h"
 #include "htlc.h"
 #include "lightning.pb-c.h"
 #include "netaddr.h"
@@ -190,6 +191,9 @@ struct peer {
 	/* All HTLCs. */
 	struct htlc_map htlcs;
 
+	/* We only track one feechange per state: last one counts. */
+	struct feechange *feechanges[FEECHANGE_STATE_INVALID];
+
 	/* Current ongoing packetflow */
 	struct io_data *io_data;