vlan: Set hard_header_len according to available acceleration

Currently, if the card supports CTAG acceleration we do not
account for the vlan header even if we are configuring an
8021AD vlan.  This may not be best since we'll do software
tagging for 8021AD which will cause data copy on skb head expansion
Configure the length based on available hw offload capabilities and
vlan protocol.

CC: Patrick McHardy <kaber@trash.net>
Signed-off-by: Vlad Yasevich <vyasevic@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>