net/mlx5: DR, select MSIX vector 0 for completion queue creation

net/mlx5: DR, select MSIX vector 0 for completion queue creation

When creating a software steering completion queue (CQ), an arbitrary
MSIX vector n is selected. This results in the CQ sharing the same
Ethernet traffic channel n associated with the chosen vector. However,
the value of n is often unpredictable, which can introduce complications
for interrupt monitoring and verification tools.

Moreover, SW steering uses polling rather than event-driven interrupts.
Therefore, there is no need to select any MSIX vector other than the
existing vector 0 for CQ creation.

In light of these factors, and to enhance predictability, we modify the
code to consistently select MSIX vector 0 for CQ creation.

Fixes: 297cccebdc5a ("net/mlx5: DR, Expose an internal API to issue RDMA operations")
Signed-off-by: Shahar Shitrit <shshitrit@nvidia.com>
Reviewed-by: Yevgeny Kliteynik <kliteyn@nvidia.com>
Signed-off-by: Tariq Toukan <tariqt@nvidia.com>
Link: https://patch.msgid.link/20241220081505.1286093-2-tariqt@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>