net/mlx5e: Use __set_bit for adaptive-moderation bit in RQ state

Make the code more clear by replacing the existing code with __set_bit.

Signed-off-by: Gal Pressman <galp@mellanox.com>
Signed-off-by: Tariq Toukan <tariqt@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>