net: kirkwood: updates: used eth_setenv_enetaddr api

eth_setenv_enetaddr is avaible by upper layer
using this saves 204 bytes on total image size

used Local OUI instead of Marvell OUI for
random MAC address generation logic

Signed-off-by: Prafulla Wadaskar <prafulla@marvell.com>
Signed-off-by: Ben Warren <biggerbadderben@gmail.com>