ionic: handle mac filter overflow

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>