tx: add setter for tx locktime

We need to update the psbt's global transaction simultaneously, so we
wrap access to the locktime in a method which will handle both

bitcoin/tx.c

@@ -151,6 +151,12 @@ static int elements_tx_add_fee_output(struct bitcoin_tx *tx)
 	}
 }
 
+void bitcoin_tx_set_locktime(struct bitcoin_tx *tx, u32 locktime)
+{
+	tx->wtx->locktime = locktime;
+	tx->psbt->tx->locktime = locktime;
+}
+
 int bitcoin_tx_add_input(struct bitcoin_tx *tx, const struct bitcoin_txid *txid,
 			 u32 outnum, u32 sequence, const u8 *scriptSig,
 			 struct amount_sat amount, const u8 *scriptPubkey,

bitcoin/tx.h

@@ -77,6 +77,9 @@ int bitcoin_tx_add_output(struct bitcoin_tx *tx, const u8 *script,
 int bitcoin_tx_add_multi_outputs(struct bitcoin_tx *tx,
 				 struct bitcoin_tx_output **outputs);
 
+/* Set the locktime for a transaction */
+void bitcoin_tx_set_locktime(struct bitcoin_tx *tx, u32 locktime);
+
 /* Add a new input to a bitcoin tx.
  *
  * For P2WSH inputs, we'll also store the wscript and/or scriptPubkey

channeld/commit_tx.c

@@ -276,8 +276,8 @@ struct bitcoin_tx *commit_tx(const tal_t *ctx,
 	 *
 	 * * locktime: upper 8 bits are 0x20, lower 24 bits are the lower 24 bits of the obscured commitment number
 	 */
-	tx->wtx->locktime
-		= (0x20000000 | (obscured_commitment_number & 0xFFFFFF));
+	bitcoin_tx_set_locktime(tx,
+	    (0x20000000 | (obscured_commitment_number & 0xFFFFFF)));
 
 	/* BOLT #3:
 	 *

common/initial_commit_tx.c

@@ -228,8 +228,8 @@ struct bitcoin_tx *initial_commit_tx(const tal_t *ctx,
 	 * * locktime: upper 8 bits are 0x20, lower 24 bits are the
 	 * lower 24 bits of the obscured commitment number
 	 */
-	tx->wtx->locktime =
-	    (0x20000000 | (obscured_commitment_number & 0xFFFFFF));
+	bitcoin_tx_set_locktime(tx,
+	    (0x20000000 | (obscured_commitment_number & 0xFFFFFF)));
 
 	/* BOLT #3:
 	 *

onchaind/test/run-grind_feerate-bug.c

@@ -357,7 +357,7 @@ struct bitcoin_tx *htlc_timeout_tx(const tal_t *ctx,
 	psbt_input_set_prev_utxo_wscript(tx->psbt, 0, commit_wscript, in_amount);
 	tx->chainparams = chainparams;
 
-	tx->wtx->locktime = cltv_expiry;
+	bitcoin_tx_set_locktime(tx, cltv_expiry);
 	return tx;
 }