chaintopology: add notify_feerate_change() callback.

We'll use this to tell peers to change feerate.

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

lightningd/chaintopology.c

@@ -303,10 +303,14 @@ static void update_feerates(struct bitcoind *bitcoind,
 			    const u32 *satoshi_per_kw,
 			    struct chain_topology *topo)
 {
+	u32 old_feerates[NUM_FEERATES];
+	bool changed = false;
+
 	for (size_t i = 0; i < NUM_FEERATES; i++) {
 		log_debug(topo->log, "%s feerate %u (was %u)",
 			  feerate_name(i),
 			  satoshi_per_kw[i], topo->feerate[i]);
+		old_feerates[i] = topo->feerate[i];
 		topo->feerate[i] = satoshi_per_kw[i];
 	}
 
@@ -320,7 +324,12 @@ static void update_feerates(struct bitcoind *bitcoind,
 				topo->feerate[j] = topo->feerate[i];
 			}
 		}
+		if (topo->feerate[i] != old_feerates[i])
+			changed = true;
 	}
+
+	if (changed)
+		notify_feerate_change(bitcoind->ld);
 }
 
 /* B is the new chain (linked by ->next); update topology */

lightningd/chaintopology.h

@@ -164,6 +164,7 @@ void setup_topology(struct chain_topology *topology,
 struct txlocator *locate_tx(const void *ctx, const struct chain_topology *topo, const struct sha256_double *txid);
 
 void notify_new_block(struct lightningd *ld, unsigned int height);
+void notify_feerate_change(struct lightningd *ld);
 
 #if DEVELOPER
 void json_dev_broadcast(struct command *cmd,

lightningd/peer_htlcs.c

@@ -1522,3 +1522,8 @@ void notify_new_block(struct lightningd *ld, u32 height)
 	/* Iteration while removing is safe, but can skip entries! */
 	} while (removed);
 }
+
+void notify_feerate_change(struct lightningd *ld)
+{
+	/* FIXME: Do something! */
+}