Set BUFFER_TX_WEIGHT to correct value

We are obviously still in the LN-DLC branch, but the buffer
transaction is smaller for vanilla DLC channels.

This change is only needed because we are not back on `master`.

dlc/src/channel/mod.rs

@@ -26,14 +26,14 @@ pub mod sub_channel;
  * scriptSig -> 0
  * nSequence -> 4 * 4
  * Witness item count -> 1
- * Witness -> 366
+ * Witness -> 220
  * OUTPUT:
  * nValue -> 8 * 4
  * scriptPubkeyLen -> 1 * 4
  * scriptPubkey -> 34 * 4
  * TOTAL: 599
 */
-pub const BUFFER_TX_WEIGHT: usize = 748;
+pub const BUFFER_TX_WEIGHT: usize = 599;
 
 /**
  * Due to the buffer output script being more complex than the funding output