net/mlx5e: Make mlx5e_modify_rqs_vsd a static function

Make mlx5e_modify_rqs_vsd a static function and remove from en.h in
order to reduce redundant exposure of functions.

Signed-off-by: Guy Ergas <guye@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>