net/mlx5e: Reduce number of arguments in slow path handling

mlx5e_tc_offload_to_slow_path() and mlx5e_tc_unoffload_from_slow_path()
take an extra argument allocated on the stack of the caller but not used
by the caller. Avoid the extra argument and use local variable in the
function itself.

Signed-off-by: Eli Cohen <eli@mellanox.com>
Reviewed-by: Roi Dayan <roid@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>