btu_hcif_send_cmd实现细节

bluedroid协议栈中所有的协议交互command 都是通过HCI发出去的，具体的实现如下：

1.btu_hcif_send_cmd

void btu_hcif_send_cmd(UNUSED_ATTR uint8_t controller_id, BT_HDR* p_buf) {
  if (!p_buf) return;

  uint16_t opcode;
  uint8_t* stream = p_buf->data + p_buf->offset;
  void* vsc_callback = NULL;

  STREAM_TO_UINT16(opcode, stream);

  // Eww...horrible hackery here
  /* If command was a VSC, then extract command_complete callback */
  if ((opcode & HCI_GRP_VENDOR_SPECIFIC) == HCI_GRP_VENDOR_SPECIFIC ||
      (opcode == HCI_BLE_RAND) || (opcode == HCI_BLE_ENCRYPT)) {
    vsc_callback = *((void**)(p_buf + 1));
  }

  // Skip parameter length before logging
  str