Revert "net/mlx5e: Update and set Xon/Xoff upon port speed set"

This reverts commit d2434174.
It causes errors when trying to configure QoS, as well as
loss of L2 connectivity (on multi-host devices).

Reported-by: Jakub Kicinski <kuba@kernel.org>
Link: https://lore.kernel.org/20250910170011.70528106@kernel.org


Fixes: d2434174 ("net/mlx5e: Update and set Xon/Xoff upon port speed set")
Signed-off-by: Tariq Toukan <tariqt@nvidia.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>