Use closest multiple of 40 as offset limit.

Author: tnull

lightning/src/routing/router.rs

@@ -1576,7 +1576,8 @@ where L::Target: Logger {
 		let max_path_offset = payment_params.max_total_cltv_expiry_delta
 			.checked_sub(path.iter().fold(0, |acc,b| b.as_ref().unwrap().cltv_expiry_delta.max(acc)))
 			.unwrap_or(shadow_ctlv_expiry_delta_offset);
-		shadow_ctlv_expiry_delta_offset = cmp::min(shadow_ctlv_expiry_delta_offset, max_path_offset);
+		shadow_ctlv_expiry_delta_offset = cmp::min(shadow_ctlv_expiry_delta_offset, 
+												   max_path_offset.checked_sub(max_path_offset.wrapping_rem(40)).unwrap_or(max_path_offset));
 
 		// Add 'shadow' CLTV offset to all hops but the final one
 		for h in path {