dev_open -- prepare an interface for use.
(struct net_device * dev);
Takes a device from down to up state. The device's private open
function is invoked and then the multicast lists are loaded. Finally
the device is moved into the up state and a NETDEV_UP message is
sent to the netdev notifier chain.
Calling this function on an active interface is a nop. On a failure
a negative errno code is returned.