nfp: abm: refuse RED offload with harddrop set

RED Qdisc will now inform the drivers about the state of the harddrop
flag.  Refuse to offload in case harddrop is set.

Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: John Hurley <john.hurley@netronome.com>
Reviewed-by: Quentin Monnet <quentin.monnet@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>