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/feechange_state.h

@@ -0,0 +1,23 @@
+#ifndef LIGHTNING_DAEMON_FEECHANGE_STATE_H
+#define LIGHTNING_DAEMON_FEECHANGE_STATE_H
+#include "config.h"
+
+/* Like HTLCs, but only adding; we never "remove" a feechange. */
+enum feechange_state {
+	/* When we add a new feechange, it goes in this order. */
+	SENT_FEECHANGE,
+	SENT_FEECHANGE_COMMIT,
+	RCVD_FEECHANGE_REVOCATION,
+	RCVD_FEECHANGE_ACK_COMMIT,
+	SENT_FEECHANGE_ACK_REVOCATION,
+
+	/* When they add a new feechange, it goes in this order. */
+	RCVD_FEECHANGE,
+	RCVD_FEECHANGE_COMMIT,
+	SENT_FEECHANGE_REVOCATION,
+	SENT_FEECHANGE_ACK_COMMIT,
+	RCVD_FEECHANGE_ACK_REVOCATION,
+
+	FEECHANGE_STATE_INVALID
+};
+#endif /* LIGHTNING_DAEMON_FEECHANGE_STATE_H */