Correct error when a peer opens a channel with a huge push_msat

The calculation uses the reserve, so we should mention it in the
error we send to our peers.

Author: TheBlueMatt

lightning/src/ln/channel.rs

@@ -1084,7 +1084,7 @@ impl<Signer: Sign> Channel<Signer> {
 		}
 		let full_channel_value_msat = (msg.funding_satoshis - msg.channel_reserve_satoshis) * 1000;
 		if msg.push_msat > full_channel_value_msat {
-			return Err(ChannelError::Close(format!("push_msat {} was larger than funding value {}", msg.push_msat, full_channel_value_msat)));
+			return Err(ChannelError::Close(format!("push_msat {} was larger than channel amount minus reserve ({})", msg.push_msat, full_channel_value_msat)));
 		}
 		if msg.dust_limit_satoshis > msg.funding_satoshis {
 			return Err(ChannelError::Close(format!("dust_limit_satoshis {} was larger than funding_satoshis {}. Peer never wants payout outputs?", msg.dust_limit_satoshis, msg.funding_satoshis)));

lightning/src/ln/functional_tests.rs

@@ -100,7 +100,7 @@ fn test_insane_channel_opens() {
 
 	insane_open_helper("Bogus channel_reserve_satoshis", |mut msg| { msg.channel_reserve_satoshis = msg.funding_satoshis + 1; msg });
 
-	insane_open_helper(r"push_msat \d+ was larger than funding value \d+", |mut msg| { msg.push_msat = (msg.funding_satoshis - msg.channel_reserve_satoshis) * 1000 + 1; msg });
+	insane_open_helper(r"push_msat \d+ was larger than channel amount minus reserve \(\d+\)", |mut msg| { msg.push_msat = (msg.funding_satoshis - msg.channel_reserve_satoshis) * 1000 + 1; msg });
 
 	insane_open_helper("Peer never wants payout outputs?", |mut msg| { msg.dust_limit_satoshis = msg.funding_satoshis + 1 ; msg });