net: ethernet: Fix the multicast IPv4 to MAC address mapping
net: ethernet: Fix the multicast IPv4 to MAC address mapping

The IPv4 multicast address to MAC address mapping was missing
the 4th byte high bit clearing.

We also need to have some storage for the multicast MAC address.
This was missing which could cause NULL pointer access.

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

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