ixgb: convert to new VLAN model

Based on a patch from Jesse Gross <jesse@nicira.com>

This switches the ixgb driver to use the new VLAN interfaces.
In doing this, it completes the work begun in
ae54496f allowing the use of
hardware VLAN insertion without having a VLAN group configured.

CC: Jesse Gross <jesse@nicira.com>
Signed-off-by: Emil Tantilov <emil.s.tantilov@intel.com>
Tested-by: Jeff Pieper <jeffrey.e.pieper@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>