llc: use dev_hard_header

Using dev_hard_header allows us to use LLC with VLANs and potentially
other Ethernet/TokernRing specific encapsulations. It also removes code
duplication between LLC and Ethernet/TokenRing core code.

Signed-off-by: Octavian Purdila <opurdila@ixiacom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>