net/mlx5e: Let channels be SD-aware

Distribute the channels between the different SD-devices to acheive
local numa node performance on multiple numas.

Each channel works against one specific mdev, creating all datapath
queues against it.

We distribute channels to mdevs in a round-robin policy.

Example for 2 mdevs and 6 channels:
+-------+---------+
| ch ix | mdev ix |
+-------+---------+
|   0   |    0    |
|   1   |    1    |
|   2   |    0    |
|   3   |    1    |
|   4   |    0    |
|   5   |    1    |
+-------+---------+

This round-robin distribution policy is preferred over another suggested
intuitive distribution, in which we first distribute one half of the
channels to mdev #0 and then the second half to mdev #1.

We prefer round-robin for a reason: it is less influenced by changes in
the number of channels. The mapping between channel index and mdev is
fixed, no matter how many channels the user configures. As the channel
stats are persistent to channels closure, changing the mapping every
single time would turn the accumulative stats less representing of the
channel's history.

Per-channel objects should stop using the primary mdev (priv->mdev)
directly, and instead move to using their own channel's mdev.

Signed-off-by: Tariq Toukan <tariqt@nvidia.com>
Reviewed-by: Gal Pressman <gal@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>