Netdev private dataroom for 6lowpan interfaces:
  
  All 6lowpan able net devices, means all interfaces with ARPHRD_6LOWPAN,
  must have "struct lowpan_priv" placed at beginning of netdev_priv.
  
  The priv_size of each interface should be calculate by:
  
   dev->priv_size = LOWPAN_PRIV_SIZE(LL_6LOWPAN_PRIV_DATA);
  
  Where LL_PRIV_6LOWPAN_DATA is sizeof linklayer 6lowpan private data struct.
  To access the LL_PRIV_6LOWPAN_DATA structure you can cast:
  
   lowpan_priv(dev)-priv;
  
  to your LL_6LOWPAN_PRIV_DATA structure.
  
  Before registering the lowpan netdev interface you must run:
  
   lowpan_netdev_setup(dev, LOWPAN_LLTYPE_FOOBAR);
  
  wheres LOWPAN_LLTYPE_FOOBAR is a define for your 6LoWPAN linklayer type of
  enum lowpan_lltypes.
  
  Example to evaluate the private usually you can do:
  
  static inline sturct lowpan_priv_foobar *
  lowpan_foobar_priv(struct net_device *dev)
  {
  	return (sturct lowpan_priv_foobar *)lowpan_priv(dev)->priv;
  }
  
  switch (dev->type) {
  case ARPHRD_6LOWPAN:
  	lowpan_priv = lowpan_priv(dev);
  	/* do great stuff which is ARPHRD_6LOWPAN related */
  	switch (lowpan_priv->lltype) {
  	case LOWPAN_LLTYPE_FOOBAR:
  		/* do 802.15.4 6LoWPAN handling here */
  		lowpan_foobar_priv(dev)->bar = foo;
  		break;
  	...
  	}
  	break;
  ...
  }
  
  In case of generic 6lowpan branch ("net/6lowpan") you can remove the check
  on ARPHRD_6LOWPAN, because you can be sure that these function are called
  by ARPHRD_6LOWPAN interfaces.