Increase CHANNEL_ANNOUNCEMENT_PROPAGATION_DELAY

The spec is being changed to keep around a channel_announcement when the
funding_txo is spent. This allows spliced channels more time to exchange
splice_locked messages before the channel is dropped from the network
graph. While LDK does not drop such channels, it uses this constant to
allow forwarding HTLCs over the channel using SCIDs from previous
funding transactions. Here, the increase from 12 to 72 reflects the spec
change.

Author: jkczyz

lightning/src/ln/channel.rs

@@ -1424,7 +1424,7 @@ pub(crate) const COINBASE_MATURITY: u32 = 100;
 /// The number of blocks to wait for a channel_announcement to propagate such that payments using an
 /// older SCID can still be relayed. Once the spend of the previous funding transaction has reached
 /// this number of confirmations, the corresponding SCID will be forgotten.
-const CHANNEL_ANNOUNCEMENT_PROPAGATION_DELAY: u32 = 12;
+const CHANNEL_ANNOUNCEMENT_PROPAGATION_DELAY: u32 = 72;
 
 struct PendingChannelMonitorUpdate {
 	update: ChannelMonitorUpdate,