mlxsw: spectrum: Offload learning to the switch ASIC

Up until now we simply stored the learning configuration of a bridge
port in the driver and decided whether to learn a new FDB record based
on this value.

However, this is sub-optimal in cases where learning is disabled on the
bridge port, as the device repeatedly generates learning notifications
for the same record.

Instead, offload the learning configuration to the device, thereby
preventing it from generating notifications when learning is disabled.

Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>