net/mlx5e: Free drop RQ in a dedicated function

The drop RQ has very limited objects to be freed, and differs
from regular RQs in the context that it is freed from.
Add a dedicated function for it, use it where needed, and remove
the drop_rq-specific checks in the generic function.

Signed-off-by: Tariq Toukan <tariqt@nvidia.com>
Reviewed-by: Aya Levin <ayal@nvidia.com>
Reviewed-by: Maxim Mikityanskiy <maximmi@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>