add ethernet to src filter (#20136)

Co-authored-by: ellensp <ellensp@ellensp-HP-ProBook-6470b.fritz.box>

platformio.ini

   -<src/feature/direct_stepping.cpp> -<src/gcode/motion/G6.cpp>
   -<src/feature/e_parser.cpp>
   -<src/feature/encoder_i2c.cpp>
+  -<src/feature/ethernet.cpp>
   -<src/feature/fanmux.cpp>
   -<src/feature/filwidth.cpp> -<src/gcode/feature/filwidth>
   -<src/feature/fwretract.cpp> -<src/gcode/feature/fwretract>