Program net device MAC addresses after initializing

Program net device MAC addresses after initializing

Add a new function to the eth_device struct for programming a network
controller's hardware address.

After all network devices have been initialized and the proper MAC address
for each has been determined, make a device driver call to program the
address into the device.  Only device instances with valid unicast addresses
will be programmed.

Signed-off-by: Ben Warren <[email protected]>
Acked-by: Detlev Zundel <[email protected]>
Tested-by: Prafulla Wadaskar <[email protected]>
Tested-by: Heiko Schocher <[email protected]>
Tested-by: Thomas Chou <[email protected]>