Portenta H7: Ethernet.h error with M4 core

Hi!
Trying to connect M4 core with a network with Ethernet, it throws me the following error:
```
C:\Users\salai\AppData\Local\Temp\arduino\sketches\CC8894BAF4C8F3E63D28F93B8DC3E5BA\libraries\Ethernet\Ethernet.cpp.o: In function `_GLOBAL__sub_I__ZN7arduino13EthernetClass5beginEPhmm':
C:\Users\salai\AppData\Local\Arduino15\packages\arduino\hardware\mbed_portenta\4.0.10\libraries\Ethernet\src/Ethernet.h:63: undefined reference to `EMAC::get_default_instance()'
collect2.exe: error: ld returned 1 exit status
```
If I delete Ethernet library inside mbed pack, it loads default Ethernet.h, compiles well but it doesn't work. I supposed it has to be something related with a recent update because some users have the [same error](https://community.platformio.org/t/portenta-m4-ethernet-compile-error/36717) (they say it worked for older versions). I have try to download older versions of mbed package and Ethernet.h but It doesn't work either.
Does someone know how to solve it or if M4 core allows Ethernet connections?
Thank you!

Start by reproducing the Portenta H7 M4-core build with the mbed_portenta 4.0.10 Ethernet library and inspect the referenced Ethernet.h and Ethernet.cpp paths around the EMAC symbol. Compare the behavior with the older mbed package versions mentioned, then verify whether Ethernet can compile and establish a network connection on the M4 core.

Written by the indexing model from the issue text.