channeld: increment fee states properly.

By iterating through them forward, we would often increment
them more than once!  Always print feestate transitions,
which is how I worked this out.

Changelog-Fixed: Protocol: handle complex feerate transitions correctly.
Signed-off-by: Rusty Russell <[email protected]>

channeld/full_channel.c

@@ -937,7 +937,6 @@ static bool fee_incstate(struct channel *channel,
 			 enum htlc_state hstate)
 {
 	int preflags, postflags;
-	const int committed_f = HTLC_FLAG(sidechanged, HTLC_F_COMMITTED);
 
 	preflags = htlc_state_flags(hstate);
 	postflags = htlc_state_flags(hstate + 1);
@@ -953,12 +952,11 @@ static bool fee_incstate(struct channel *channel,
 	if (!inc_fee_state(channel->fee_states, hstate))
 		return false;
 
-	if (!(preflags & committed_f) && (postflags & committed_f))
-		status_debug("Feerate: %s->%s %s now %u",
-			     htlc_state_name(hstate),
-			     htlc_state_name(hstate+1),
-			     side_to_str(sidechanged),
-			     *channel->fee_states->feerate[hstate+1]);
+	status_debug("Feerate: %s->%s %s now %u",
+		     htlc_state_name(hstate),
+		     htlc_state_name(hstate+1),
+		     side_to_str(sidechanged),
+		     *channel->fee_states->feerate[hstate+1]);
 	return true;
 }
 
@@ -973,7 +971,7 @@ static int change_htlcs(struct channel *channel,
 	struct htlc_map_iter it;
 	struct htlc *h;
 	int cflags = 0;
-	size_t i;
+	int i;
 	struct balance owed[NUM_SIDES];
 
 	for (i = 0; i < NUM_SIDES; i++)
@@ -1005,8 +1003,8 @@ static int change_htlcs(struct channel *channel,
 		}
 	}
 
-	/* Update fees. */
-	for (i = 0; i < n_hstates; i++) {
+	/* Update fees (do backwards, to avoid double-increment!). */
+	for (i = n_hstates - 1; i >= 0; i--) {
 		if (fee_incstate(channel, sidechanged, htlc_states[i]))
 			cflags |= (htlc_state_flags(htlc_states[i])
 				   ^ htlc_state_flags(htlc_states[i]+1));