net/eth: fix a bug in on_ethaddr()

The loop should check all ethenet devices, not only the first device,
to set each specified ethaddr, or it'll cause failure when we use other
devices.

Signed-off-by: Gong Qianyu <Qianyu.Gong@freescale.com>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>

net/eth.c

@@ -691,6 +691,7 @@ static int on_ethaddr(const char *name, const char *value, enum env_op op,
 				memset(dev->enetaddr, 0, 6);
 			}
 		}
+		dev = dev->next;
 	} while (dev != eth_devices);
 
 	return 0;