__dev_get_by_index - find a device by its ifindex
struct net_device * __dev_get_by_index (int ifindex);
ifindex index of device
Search for an interface by index. Returns NULL if the device is not found or a pointer to the device. The device has not had its reference counter increased so the caller must be careful about locking. The caller must hold either the RTNL semaphore or dev_base_lock.