Fix stale debug-flag name in companion_radio_ethernet env comment

The commented-out debug flag still referenced #1983's original macro name
(ETHERNET_DEBUG_LOGGING). SerialEthernetInterface.h now checks
ETH_DEBUG_LOGGING after the merge with our multi-client/PoE-deferred
implementation, so the comment was stale and enabling it would have done
nothing.

Co-Authored-By: Claude Sonnet 5 <[email protected]>

variants/rak4631/platformio.ini

@@ -192,7 +192,7 @@ build_flags =
   -D ETHERNET_ENABLED=1
 ; NOTE: DO NOT ENABLE -->  -D MESH_PACKET_LOGGING=1
 ; NOTE: DO NOT ENABLE -->  -D MESH_DEBUG=1
-;  -D ETHERNET_DEBUG_LOGGING=1
+;  -D ETH_DEBUG_LOGGING=1
 build_src_filter = ${rak4631.build_src_filter}
   +<../examples/companion_radio/*.cpp>
   +<../examples/companion_radio/ui-new/*.cpp>