net/mlx5e: Use tc sample stubs instead of ifdefs in source file

Instead of having sparse ifdefs in source files use a single
ifdef in the tc sample header file and use stubs.

Signed-off-by: Roi Dayan <roid@nvidia.com>
Reviewed-by: Maor Dickman <maord@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>