net/mlx5: Properly deal with flow counters when deleting rules

When deleting a flow counter, the modify mask should be the action and
the flow counter. Otherwise the flow counter is not deleted and we'll
get a firmware warning when deleting the remaining destinations on the
same FTE.

It only happens in the presence of flow counter and multiple vport
destinations. If there is only one vport destination, there is no
need to update the FTE when deleting the only vport destination,
we just delete the FTE.

Fixes: ae058314 ("net/mlx5: Add option to add fwd rule with counter")
Signed-off-by: Chris Mi <chrism@mellanox.com>
Signed-off-by: Jianbo Liu <jianbol@mellanox.com>
Reviewed-by: Mark Bloch <markb@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>