net/mlx4_en: Avoid adding steering rules with invalid ring

Inserting steering rules with illegal ring is an invalid operation,
block it.

Fixes: 82067281 ('net/mlx4_en: Manage flow steering rules with ethtool')
Signed-off-by: Talat Batheesh <talatb@mellanox.com>
Signed-off-by: Tariq Toukan <tariqt@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>