net/mlx5e: Support multiple RSS contexts

net/mlx5e: Support multiple RSS contexts

Add support to multiple RSS contexts. Resources of the non-default
RSS contexts are allocated and created on demand. Each RSS context
can be controlled and configured separately, via the implemented
ethtool ops. Here we limit the num of total contexts to 16.

We do not enforce any kind of new limitation over the indirection table
content. More specifically, two separate contexts can be configured to
fully or partially point to the same set of receive rings.

The default RSS context (index 0) is created with its full set of TIRs.
All other contexts are created with an empty set, then TIRs are added
upon first usage when steering rules are added.
We use a reference counting mechanism to make sure an RSS context is
not removed before the rules pointing to it.

Block ethtool set_channels operations when multiple RSS contexts exist,
as currently the kernel doesn't protect against inconsistent channels
configs that break non-default RSS contexts.

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