Make sure we go into PROMISC mode when we have too many
filters by specifically counting the filters that successfully
get saved to the firmware.

The device advertises max_ucast_filters and max_mcast_filters,
but really only has max_ucast_filters slots available for
uc and mc filters combined.
Signed-off-by: Shannon Nelson <snelson@pensando.io>
Signed-off-by: David S. Miller <davem@davemloft.net>