net/mlx5: check device status before creating flow

net/mlx5: check device status before creating flow

By default, flows are categorized into two types of a mlx5 device.
  1. The PMD driver will create some default flows to enable the
     traffic and give some default behaviors on the packets. And
     this is transparent to the upper layer application.
  2. Other flows will be created in the application based on its
     needs.
When in the old cached mode for application flows, it is allowed
to created the flow before the device is started. And when
starting the device, all the flows will be applied to the hardware
and take effect. The cached flows will be also applied in the same
time.
In non-cached mode, all the flows will never be cached when stopping
a device. So it makes no sense to insert any flow into the device
before it is started. Default flows owned by PMD driver are not
affected in this case.

Signed-off-by: Bing Zhao <bingz@mellanox.com>
Acked-by: Matan Azrad <matan@mellanox.com>