Bluetooth: controller: Fix data PDU leak during ctrl PDU defer

Fix a bug where in tx data PDU enqueued, while a ctrl PDU is
deferred due to Encryption setup being in progress, is
leaked causing HCI Tx Buffer Overflow crash.

Signed-off-by: Vinayak Kariappa Chettimada <vich@nordicsemi.no>

subsys/bluetooth/controller/ll_sw/ctrl.c

@@ -10076,6 +10076,11 @@ static void ctrl_tx_sec_enqueue(struct connection *conn,
 			node_tx->next = conn->pkt_tx_ctrl_last->next;
 			conn->pkt_tx_ctrl_last->next = node_tx;
 		}
+
+		/* Update last pointer if ctrl added at end of tx list */
+		if (!node_tx->next) {
+			conn->pkt_tx_last = node_tx;
+		}
 	} else {
 		bool pause = false;