closingd: use the final commitment tx fee as the maximum.

We shouldn't fail negotiation just because they exceeded what we thought
fair: we're better off as long as it's actually <= final commitment fee.

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

closingd/closing.c

@@ -168,7 +168,7 @@ int main(int argc, char *argv[])
 	u16 funding_txout;
 	u64 funding_satoshi, satoshi_out[NUM_SIDES];
 	u64 our_dust_limit;
-	u64 minfee, maxfee, sent_fee;
+	u64 minfee, feelimit, maxfee, sent_fee;
 	s64 last_received_fee = -1;
 	enum side funder;
 	u8 *scriptpubkey[NUM_SIDES], *funding_wscript;

closingd/closing_wire.csv

@@ -14,7 +14,7 @@ closing_init,,local_msatoshi,u64
 closing_init,,remote_msatoshi,u64
 closing_init,,our_dust_limit,u64
 closing_init,,min_fee_satoshi,u64
-closing_init,,max_fee_satoshi,u64
+closing_init,,fee_limit_satoshi,u64
 closing_init,,initial_fee_satoshi,u64
 closing_init,,local_scriptpubkey_len,u16
 closing_init,,local_scriptpubkey,local_scriptpubkey_len*u8

lightningd/peer_control.c

@@ -1888,7 +1888,7 @@ static void peer_start_closingd(struct peer *peer,
 {
 	const tal_t *tmpctx = tal_tmpctx(peer);
 	u8 *initmsg, *local_scriptpubkey;
-	u64 minfee, maxfee, startfee, feelimit;
+	u64 minfee, startfee, feelimit;
 	u64 num_revocations;
 	u64 funding_msatoshi, our_msatoshi, their_msatoshi;
 
@@ -1936,15 +1936,11 @@ static void peer_start_closingd(struct peer *peer,
 	feelimit = commit_tx_base_fee(peer->channel_info->feerate_per_kw[LOCAL],
 				      0);
 
-	maxfee = commit_tx_base_fee(get_feerate(peer->ld->topology,
-						FEERATE_IMMEDIATE), 0);
 	minfee = commit_tx_base_fee(get_feerate(peer->ld->topology,
 						FEERATE_SLOW), 0);
 	startfee = commit_tx_base_fee(get_feerate(peer->ld->topology,
 						  FEERATE_NORMAL), 0);
 
-	if (maxfee > feelimit)
-		maxfee = feelimit;
 	if (startfee > feelimit)
 		startfee = feelimit;
 	if (minfee > feelimit)
@@ -1974,7 +1970,7 @@ static void peer_start_closingd(struct peer *peer,
 				      our_msatoshi / 1000, /* Rounds down */
 				      their_msatoshi / 1000, /* Rounds down */
 				      peer->our_config.dust_limit_satoshis,
-				      minfee, maxfee, startfee,
+				      minfee, feelimit, startfee,
 				      local_scriptpubkey,
 				      peer->remote_shutdown_scriptpubkey,
 				      reconnected,