8021q: set hard_header_len when VLAN offload features are toggled

Toggling the vlan tx|rx hw offloads needs to set the hard_header_len
as well otherwise we end up using LL_RESERVED_SPACE incorrectly.
This results in pskb_expand_head() being used unnecessarily.

Signed-off-by: John Fastabend <john.r.fastabend@intel.com>
Acked-by: Jesse Gross <jesse@nicira.com>
Signed-off-by: David S. Miller <davem@davemloft.net>