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

Implement devlink port function commands to enable / disable RoCE.
This is used to control the RoCE device capabilities.

This patch implement infrastructure which will be used by downstream
patches that will add additional capabilities.

Signed-off-by: Yishai Hadas <yishaih@nvidia.com>
Signed-off-by: Daniel Jurgens <danielj@nvidia.com>
Signed-off-by: Shay Drory <shayd@nvidia.com>
Reviewed-by: Parav Pandit <parav@nvidia.com>
Reviewed-by: Mark Bloch <mbloch@nvidia.com>
Acked-by: Saeed Mahameed <saeedm@nvidia.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>