drivers: eth: native_posix: Fix gPTP header parsing
drivers: eth: native_posix: Fix gPTP header parsing

We were reading gPTP header from wrong position when parsing
it in RX and TX.

Signed-off-by: Jukka Rissanen <f9f077d1da4c7aa947f9864fa5a28c3588f6a45d@linux.intel.com>

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