i40e: move check for avoiding VID=0 filters into i40e_vsi_add_vlan

In i40e_vsi_add_vlan we treat attempting to add VID=0 as an error,
because it does not do what the caller might expect. We already special
case VID=0 in i40e_vlan_rx_add_vid so that we avoid this error when
adding the VLAN.

This special casing is necessary so that we do not add the VLAN=0 filter
since we don't want to stop receiving untagged traffic. Unfortunately,
not all callers of i40e_vsi_add_vlan are aware of this, including when
we add VLANs from a VF device.

Rather than special casing every single caller of i40e_vsi_add_vlan,
lets just move this check internally. This makes the code simpler
because the caller does not need to be aware of how VLAN=0 is special,
and we don't forget to add this check in new places.

This fixes a harmless error message displaying when adding a VLAN from
within a VF. The message was meaningless but there is no reason to
confuse end users and system administrators, and this is now avoided.

Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>