net/mlx5e: debugfs, Add reset option for command interface stats

Resetting stats just before some test/debug case allows us to eliminate
out the impact of previous commands. Useful in particular for the
average latency calculation.

The average_write() callback was unreachable, as "average" is a
read-only file. Extend, rename,  and use it for a newly exposed
write-only "reset" file.

Signed-off-by: Tariq Toukan <tariqt@nvidia.com>
Reviewed-by: Saeed Mahameed <saeedm@nvidia.com>
Reviewed-by: Gal Pressman <gal@nvidia.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://lore.kernel.org/r/20240402133043.56322-6-tariqt@nvidia.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>