nimble/host: Fix unexpected assertion

This fixes unexpected assertion that happens before mutex lock.
The caller shall wait on mutex instead, when ack is pending.

Author: MariuszSkamra

nimble/host/src/ble_hs_hci.c

@@ -313,8 +313,8 @@ ble_hs_hci_cmd_tx(uint16_t opcode, const void *cmd, uint8_t cmd_len,
     struct ble_hs_hci_ack ack;
     int rc;
 
-    BLE_HS_DBG_ASSERT(ble_hs_hci_ack == NULL);
     ble_hs_hci_lock();
+    BLE_HS_DBG_ASSERT(ble_hs_hci_ack == NULL);
 
     rc = ble_hs_hci_cmd_send_buf(opcode, cmd, cmd_len);
     if (rc != 0) {