Users are not prevented from creating flow rules targeting nonexistent
queues, which silently makes such rules drop-like.
While it can be thought as a feature, reporting an error instead is
actually far more useful in order to catch common mistakes.
Fixes: 078b8b452e ("net/mlx4: add RSS flow rule action support")
Signed-off-by: Adrien Mazarguil <adrien.mazarguil@6wind.com>