net: Provide a function to get the current MAC address

The current implementation exposes the eth_device struct to code that
needs to access the MAC address.  Add a wrapper function for this to
abstract away the pointer for this operation.

Signed-off-by: Joe Hershberger <joe.hershberger@ni.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

net/net.c

@@ -275,7 +275,7 @@ static void NetInitLoop(void)
 		env_changed_id = env_id;
 	}
 	if (eth_get_dev())
-		memcpy(NetOurEther, eth_get_dev()->enetaddr, 6);
+		memcpy(NetOurEther, eth_get_ethaddr(), 6);
 
 	return;
 }