drivers/ethernet: Switch SMSC911x to new net_pkt API
drivers/ethernet: Switch SMSC911x to new net_pkt API

It was still using old allocator and net_pkt function to read/write the
data.

Signed-off-by: Tomasz Bursztyka <ba81a3a719836727e6857ae83462b9f52ec41006@linux.intel.com>

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