net/mlx5e: increase RSS indirection table spread factor

Increase the RQT uniform spread factor from 2 to 4 so that each channel
gets more indirection table entries and traffic is spread more evenly.
For num_channels > 64 imbalance drops from up to ~50% to up to ~25%.
For 64 or fewer channels the 256 entry minimum already provides at least
4x coverage and the table size is unchanged by this commit.

This satisfies the minimum 4x coverage requirement validated by the
generic RSS selftest commit 9e3d4dae98 ("selftests: drv-net: rss:
validate min RSS table size").

The 4x spread factor is best-effort and the table size is always capped by
the device's log_max_rqt_size capability.

Signed-off-by: Yael Chemla <ychemla@nvidia.com>
Reviewed-by: Nimrod Oren <noren@nvidia.com>
Signed-off-by: Tariq Toukan <tariqt@nvidia.com>
Link: https://patch.msgid.link/20260511172719.330490-6-tariqt@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/mellanox/mlx5/core/en/rqt.h

@@ -7,7 +7,7 @@
 #include <linux/kernel.h>
 
 #define MLX5E_INDIR_MIN_RQT_SIZE (BIT(8))
-#define MLX5E_UNIFORM_SPREAD_RQT_FACTOR 2
+#define MLX5E_UNIFORM_SPREAD_RQT_FACTOR 4
 
 struct mlx5_core_dev;