igb: Add workaround for VLAN tag stripping on 82576

There was a workaround partially implemented for the 82576 that is needed
in order for VLAN tag stripping to function correctly.  The original code
had side effects that would make it so the workaround was active on all
MACs.  I have updated the code so that the workaround is enabled, but
limited to the 82576, or activated if we exceed the available unicast
addresses.

The workaround has a side effect of mirroring all of the traffic outgoing
from the VFs back to the PF.  As such it is not recommended to use the
82576 in promiscuous mode as it will take a performance hit, though this is
now consistent with the performance as seen on the out-of-tree igb driver.

I also limited the scope of the UTA bits all being set to only when the
VMOLR register is enabled.  This should limit the effects of the UTA
register so that we don't pick up any excess traffic unless promiscuous
mode has been enabled on the PF, whereas before the PF would have ended up
in something equivalent to unicast promiscuous mode with VLAN filtering
otherwise.

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>