Add cltv expiry to PendingHTLCRouting::Forward

This is needed to add cltv expiry to HTLCSource::PreviousHopData in an
upcoming commit.

Author: alecchendev

lightning/src/ln/channelmanager.rs

@@ -104,6 +104,7 @@ pub(super) enum PendingHTLCRouting {
 		/// The SCID from the onion that we should forward to. This could be a real SCID or a fake one
 		/// generated using `get_fake_scid` from the scid_utils::fake_scid module.
 		short_channel_id: u64, // This should be NonZero<u64> eventually when we bump MSRV
+		incoming_cltv_expiry: Option<u32>,
 	},
 	Receive {
 		payment_data: msgs::FinalOnionHopData,
@@ -3002,6 +3003,7 @@ where
 					routing: PendingHTLCRouting::Forward {
 						onion_packet: outgoing_packet,
 						short_channel_id,
+						incoming_cltv_expiry: Some(msg.cltv_expiry),
 					},
 					payment_hash: msg.payment_hash.clone(),
 					incoming_shared_secret: shared_secret,
@@ -3669,8 +3671,9 @@ where
 			})?;
 
 		let routing = match payment.forward_info.routing {
-			PendingHTLCRouting::Forward { onion_packet, .. } => {
-				PendingHTLCRouting::Forward { onion_packet, short_channel_id: next_hop_scid }
+			PendingHTLCRouting::Forward { onion_packet, incoming_cltv_expiry, .. } => {
+				PendingHTLCRouting::Forward { onion_packet, short_channel_id: next_hop_scid,
+					incoming_cltv_expiry }
 			},
 			_ => unreachable!() // Only `PendingHTLCRouting::Forward`s are intercepted
 		};
@@ -7615,6 +7618,7 @@ impl_writeable_tlv_based!(PhantomRouteHints, {
 impl_writeable_tlv_based_enum!(PendingHTLCRouting,
 	(0, Forward) => {
 		(0, onion_packet, required),
+		(1, incoming_cltv_expiry, option),
 		(2, short_channel_id, required),
 	},
 	(1, Receive) => {