Select the channel with the highest balance for blinded paths

When building a compact blinded path we need to pick a channel for
an SCID that we think is mostl likely to stick around the longest.
We don't really have any great options cause we have no idea what
downstream code does, but "highest balance" seems marginally
better than the previous criteria of "oldest channel".

Author: TheBlueMatt

lightning/src/ln/channelmanager.rs

@@ -14085,7 +14085,9 @@ impl<
 					short_channel_id: peer_chans
 						.iter()
 						.filter(|chan| chan.is_usable)
-						.min_by_key(|chan| chan.short_channel_id)
+						// Select the channel which has the highest local balance. We assume this
+						// channel is the most likely to stick around.
+						.max_by_key(|chan| chan.inbound_capacity_msat)
 						.and_then(|chan| chan.get_inbound_payment_scid()),
 				})
 			}
@@ -14108,7 +14110,9 @@ impl<
 					.iter()
 					.filter(|(_, channel)| channel.context().is_usable())
 					.filter_map(|(_, channel)| channel.as_funded())
-					.min_by_key(|funded_channel| funded_channel.context.channel_creation_height)
+					// Select the channel which has the highest local balance. We assume this
+					// channel is the most likely to stick around.
+					.max_by_key(|funded_channel| funded_channel.funding.get_value_to_self_msat())
 					.and_then(|funded_channel| funded_channel.get_inbound_scid()),
 			})
 			.collect::<Vec<_>>()