Possible memory problems with Ethernet and CDC-ACM

It seems like while running [teensy-4.x:netnsh-4.1](https://github.com/apache/incubator-nuttx/blob/master/boards/arm/imxrt/teensy-4.x/configs/netnsh-4.1/defconfig) configuration (ethernet + console over CDC-ACM) a huge memory leak occurs:

```
nsh> free
total used free largest
Umem: 751616 218779424 0 0
nsh>
```
This is state after one printed ifconfig, another one results in fault and it´s necessary to reload NuttX (sometimes the fault occurs even with the first ifconfig). Ethernet configuration with console over UART is working fine, also another configurations over CDC-ACM are ok ([lcd-4.1](https://github.com/apache/incubator-nuttx/blob/master/boards/arm/imxrt/teensy-4.x/configs/lcd-4.1/defconfig) or [can-4.1](https://github.com/apache/incubator-nuttx/blob/master/boards/arm/imxrt/teensy-4.x/configs/can-4.1/defconfig)). The problems seems to occur only after running ifconfig command in netnsh-4.1.

Unfortunately I don´t have any other board I could connect with CDC-ACM so could someone check ethernet + console over CDC-ACM with a different board so we would know whether the problem is just Teensy related or it´s something in network? Thanks.