f const-ify overpay estimate multiplier

Author: valentinewallace

lightning/src/ln/onion_utils.rs

@@ -328,8 +328,9 @@ pub(crate) fn set_max_path_length(
 	.serialized_length()
 	.saturating_add(PAYLOAD_HMAC_LEN);
 
+	const OVERPAY_ESTIMATE_MULTIPLER: u64 = 3;
 	let final_value_msat_with_overpay_buffer = core::cmp::max(
-		route_params.final_value_msat.saturating_mul(4),
+		route_params.final_value_msat.saturating_mul(OVERPAY_ESTIMATE_MULTIPLER),
 		MIN_FINAL_VALUE_ESTIMATE_WITH_OVERPAY,
 	);