channel: fix max feelevel calculation.

We were out by 1000, and also derived it from the previous, not current
state.

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

daemon/channel.c

@@ -172,7 +172,7 @@ uint64_t approx_max_feerate(const struct channel_state *cstate,
 
 	max_funds = cstate->side[side].pay_msat + cstate->side[side].fee_msat;
 
-	return max_funds * 1000 / tx_bytes(cstate->num_nondust);
+	return max_funds / tx_bytes(cstate->num_nondust);
 }
 
 bool can_afford_feerate(const struct channel_state *cstate, uint64_t fee_rate,

daemon/peer.c

@@ -2119,7 +2119,8 @@ static void maybe_propose_new_feerate(struct peer *peer)
 	u64 rate, max_rate;
 
 	rate = desired_commit_feerate(peer->dstate);
-	max_rate = approx_max_feerate(peer->remote.commit->cstate, LOCAL);
+	max_rate = approx_max_feerate(peer->remote.staging_cstate, LOCAL);
+	assert(can_afford_feerate(peer->remote.staging_cstate, max_rate, LOCAL));
 
 	/* BOLT #2:
 	 *