dev_alloc_name — allocate a name for a device
| int dev_alloc_name ( | struct net_device * dev, | 
| const char * name ); | 
   Passed a format string - eg “ltd” it will try and find a suitable
   id. It scans list of devices to build up a free map, then chooses
   the first empty slot. The caller must hold the dev_base or rtnl lock
   while allocating the name and adding the device in order to avoid
   duplicates.
   Limited to bits_per_byte * page size devices (ie 32K on most platforms).
   Returns the number of the unit assigned or a negative errno code.