native: doc eth TAP: can only be compiled in Unix
native: doc eth TAP: can only be compiled in Unix

Minor change in eth tap interface, as it can only be compiled
in Unix

Signed-off-by: Alberto Escolar Piedras <52be3174920ed06cbdfbcf9622a1a6c68e942617@oticon.com>

zephyriot/zephyr,explora26/zephyr,GiulianoFranchetto/zephyr,Vudentz/zephyr,punitvara/zephyr,zephyriot/zephyr,punitvara/zephyr,nashif/zephyr,punitvara/zephyr,explora26/zephyr,nashif/zephyr,galak/zephyr,explora26/zephyr,mbolivar/zephyr,mbolivar/zephyr,Vudentz/zephyr,zephyrproject-rtos/zephyr,GiulianoFranchetto/zephyr,zephyriot/zephyr,GiulianoFranchetto/zephyr,galak/zephyr,ldts/zephyr,kraj/zephyr,explora26/zephyr,Vudentz/zephyr,kraj/zephyr,finikorg/zephyr,finikorg/zephyr,kraj/zephyr,zephyriot/zephyr,Vudentz/zephyr,Vudentz/zephyr,kraj/zephyr,mbolivar/zephyr,ldts/zephyr,finikorg/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,nashif/zephyr,ldts/zephyr,punitvara/zephyr,GiulianoFranchetto/zephyr,zephyrproject-rtos/zephyr,mbolivar/zephyr,ldts/zephyr,zephyrproject-rtos/zephyr,mbolivar/zephyr,galak/zephyr,ldts/zephyr,punitvara/zephyr,kraj/zephyr,Vudentz/zephyr,explora26/zephyr,zephyriot/zephyr,galak/zephyr,nashif/zephyr,finikorg/zephyr,GiulianoFranchetto/zephyr,nashif/zephyr