ixgbe: Allow FDB entries access to more RAR filters

This change makes it so that we allow the PF to make use of all free RAR
entries for FDB use if needed.

Previously the code limited us to 16 unicast entries, however this was
shared between MACVLAN which wasn't limited and the FDB code which was.  So
instead of treating the FDB code as a second class citizen I have updated
it so that it has access to just as many entries as the MACVLAN filters.

Signed-off-by: Alexander Duyck <aduyck@mirantis.com>
Tested-by: Darin Miller <darin.j.miller@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>