net/mlx4_en: Move filters cleanup to a proper location

Filters cleanup should be done once before destroying net device,
since filters list is contained in the private data.

Fixes: 1eb8c695

 ('net/mlx4_en: Add accelerated RFS support')
Signed-off-by: Eugenia Emantayev <eugenia@mellanox.com>
Signed-off-by: Tariq Toukan <tariqt@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>