net/mlx5e: Update and set Xon/Xoff upon MTU set

net/mlx5e: Update and set Xon/Xoff upon MTU set

Xon/Xoff sizes are derived from calculation that include the MTU size.
Set Xon/Xoff when MTU is set.
If Xon/Xoff fails, set the previous MTU.

Fixes: 0696d60853d5 ("net/mlx5e: Receive buffer configuration")
Signed-off-by: Alexei Lazar <alazar@nvidia.com>
Reviewed-by: Tariq Toukan <tariqt@nvidia.com>
Signed-off-by: Mark Bloch <mbloch@nvidia.com>
Link: https://patch.msgid.link/20250825143435.598584-10-mbloch@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>