igb: Enable use of "bridge fdb add" to set unicast table entries

This change makes it so that we can use the bridge utility to add a FDB
entry for the PF to an igb port.  By doing this we can enable the VFs to
talk to virtual ports residing on top of the PF.

In addition this should also address issues with MACVLANs trying to reside
on top of the PF as well as they would have had similar issues when added
to the PF with SR-IOV enabled.

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>