net/mlx5: E-Switch, Implement devlink port function cmds to control migratable

Implement devlink port function commands to enable / disable migratable.
This is used to control the migratable capability of the device.

Signed-off-by: Shay Drory <shayd@nvidia.com>
Reviewed-by: Mark Bloch <mbloch@nvidia.com>
Acked-by: Saeed Mahameed <saeedm@nvidia.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>