igb: Always enable VLAN 0 even if 8021q is not loaded

This patch makes it so that we always add VLAN 0.  This is important as we
need to guarantee the PF can receive untagged frames in the case of SR-IOV
being enabled but VLAN filtering not being enabled in the kernel.

Signed-off-by: Alexander Duyck <aduyck@mirantis.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>