eth: fbnic: set IFF_UNICAST_FLT to avoid enabling promiscuous mode when adding unicast addrs

I realized when we were adding unicast addresses we were enabling
promiscuous mode. I did a bit of digging and realized we had overlooked
setting the driver private flag to indicate we supported unicast filtering.

Example below shows the table with 00deadbeef01 as the main NIC address,
and 5 additional addresses in the 00deadbeefX0 format.

  # cat $dbgfs/mac_addr
  Idx S TCAM Bitmap       Addr/Mask
  ----------------------------------
  00  0 00000000,00000000 000000000000
                          000000000000
  01  0 00000000,00000000 000000000000
                          000000000000
  02  0 00000000,00000000 000000000000
                          000000000000
  ...
  24  0 00000000,00000000 000000000000
                          000000000000
  25  1 00100000,00000000 00deadbeef50
                          000000000000
  26  1 00100000,00000000 00deadbeef40
                          000000000000
  27  1 00100000,00000000 00deadbeef30
                          000000000000
  28  1 00100000,00000000 00deadbeef20
                          000000000000
  29  1 00100000,00000000 00deadbeef10
                          000000000000
  30  1 00100000,00000000 00deadbeef01
                          000000000000
  31  0 00000000,00000000 000000000000
                          000000000000

Before rule 31 would be active. With this change it correctly sticks
to just the unicast filters.

Signed-off-by: Alexander Duyck <alexanderduyck@meta.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20250204010038.1404268-2-kuba@kernel.org


Signed-off-by: Paolo Abeni <pabeni@redhat.com>