net/mlx5: create global drop action

net/mlx5: create global drop action

This commit creates the global drop action for flows instead of
maintain it in flow insertion time. The uniqueu global drop action
makes it thread safe.

Signed-off-by: Suanming Mou <suanmingm@nvidia.com>
Acked-by: Matan Azrad <matan@nvidia.com>