net/mlx5e: Split out channel (de)activation in rx_res

To decrease the nesting level and reduce duplication of code, create
functions to redirect direct RQTs to the actual RQs or drop_rq, which
are used in the activation and deactivation flows of channels.

Signed-off-by: Maxim Mikityanskiy <maximmi@nvidia.com>
Reviewed-by: Saeed Mahameed <saeedm@nvidia.com>
Reviewed-by: Tariq Toukan <tariqt@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>