ixgbe: Re-enable ability to toggle VLAN filtering

Back when I submitted the GSO code I messed up and dropped the support for
disabling the VLAN tag filtering via the feature bit.  This patch
re-enables the use of the NETIF_F_HW_VLAN_CTAG_FILTER to enable/disable the
VLAN filtering independent of toggling promiscuous mode.

Fixes: b83e3010

 ("ixgbe/ixgbevf: Add support for GSO partial")
Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>