net/mlx5e: Allow SQ outside of channel context

In order to be able to create an SQ outside of a channel context, remove
sq->channel direct pointer. This requires adding a direct pointer to:
netdevice, priv and mlx5_core in order to support SQs that are part of
mlx5e_channel. Use channel_stats from the corresponding CQ.

Signed-off-by: Eran Ben Elisha <eranbe@nvidia.com>
Signed-off-by: Aya Levin <ayal@nvidia.com>
Reviewed-by: Tariq Toukan <tariqt@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>