mlxsw: spectrum_acl: Do not report activity for multicast routes

The driver periodically queries the device for activity of ACL rules in
order to report it to tc upon 'FLOW_CLS_STATS'.

In Spectrum-2 and later ASICs, multicast routes are programmed as ACL
rules, but unlike rules installed by tc, their activity is of no
interest.

Avoid unnecessary activity query for such rules by always reporting them
as inactive.

Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Reviewed-by: Petr Machata <petrm@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>