net: sch: red: Change the name of the stats struct to be generic

Change the name of the stats struct to be generic, so it could be used for
other qdisc offload, that will be added in the next patches.

Signed-off-by: Nogah Frankel <nogahf@mellanox.com>
Reviewed-by: Yuval Mintz <yuvalm@mellanox.com>
Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>