Add warning about NO_ETHERNET_TURN_OFF

[alrvid]

Adds a warning that improper use of this #define can damage the Ethernet transmission termination resistors.

[github-actions]

Memory usage change @ 37177c3

Board	flash	%	RAM for global variables	%
arduino:mbed_portenta:envie_m7	N/A	N/A	N/A	N/A

Click for full report table

Board	examples/AllowDeepSleep flash	%	examples/AllowDeepSleep RAM for global variables	%	examples/DeepSleepLockDebug flash	%	examples/DeepSleepLockDebug RAM for global variables	%	examples/Standby flash	%	examples/Standby RAM for global variables	%
arduino:mbed_portenta:envie_m7	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A

Click for full report CSV

Board,examples/AllowDeepSleep<br>flash,%,examples/AllowDeepSleep<br>RAM for global variables,%,examples/DeepSleepLockDebug<br>flash,%,examples/DeepSleepLockDebug<br>RAM for global variables,%,examples/Standby<br>flash,%,examples/Standby<br>RAM for global variables,%
arduino:mbed_portenta:envie_m7,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A

[facchinm]

Would it be nice to add something like

#if defined(NO_ETHERNET_TURN_OFF)
#warning "Please check the documentation before using this functionality"
#endif

in case the user didn't read the info in advance?

[alrvid]

Would it be nice to add something like

#if defined(NO_ETHERNET_TURN_OFF)
#warning "Please check the documentation before using this functionality"
#endif

in case the user didn't read the info in advance?

I just added that to the other open PR. Thanks! :-)