[PATCH v2] net/mlx5: add stub functions to null drv ops

[Matan Azrad]

From: Asaf Penso <asafp at nvidia.com>
> There are several functions implementation that queries the drv type to
> understand which fops function to use.
> In case the type is DV, the function gets the concrete DV function and calls it.
> In case it’s not, the function returns an error.
> 
> The current implementation is not flexible enough and will not support future
> concrete functions in a good way.
> 
> This patch adds more stub functions that include error handling and are assigned
> to the null drv ops struct.
> This allows the functions to always call the virtual function without basing the
> decision on a specific drv type.
> 
> Signed-off-by: Asaf Penso <asafp at nvidia.com>
Acked-by: Matan Azrad <matan at nvidia.com>