ixgbe_xmit_frame can be refactored to use fewer locals and better
utilize common kernel macros.

also fixed minor buglet with internal to driver vlan flag variable being
passed incorrectly.
Signed-off-by: NJesse Brandeburg <jesse.brandeburg@intel.com>
Signed-off-by: NJeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: NJeff Garzik <jgarzik@redhat.com>