i40evf: use capabilities flags properly

Use the capabilities passed to us by the PF driver to control VF driver
behavior. In the process, clean up the VLAN add/remove code so it's not
a horrible morass of ifdefs.

Change-ID: I1050eaf12b658a26fea6813047c9964163c70a73
Signed-off-by: Mitch Williams <mitch.a.williams@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>