Fix the crash in kernel while dereferencing the NULL pointer,
when the driver is unloaded and simultaneously the VSI rings
are being stopped.

The hardware requires 50msec in order to finish RX queues
disable. For this purpose the driver spins in mdelay function
for the operation to be completed.

For example changing number of queues which requires reset would
fail in the following call stack:

1) i40e_prep_for_reset
2) i40e_pf_quiesce_all_vsi
3) i40e_quiesce_vsi
4) i40e_vsi_close
5) i40e_down
6) i40e_vsi_stop_rings
7) i40e_vsi_control_rx -> disable requires the delay of 50msecs
8) continue back in i40e_down function where
   i40e_clean_tx_ring(vsi->tx_rings[i]) is going to crash

When the driver was spinning vsi_release called
i40e_vsi_free_arrays where the vsi->tx_rings resources
were freed and the pointer was set to NULL.

Fixes: 5b6d4a7f ("i40e: Fix crash during removing i40e driver")
Signed-off-by: NSlawomir Laba <slawomirx.laba@intel.com>
Signed-off-by: NSylwester Dziedziuch <sylwesterx.dziedziuch@intel.com>
Signed-off-by: NKaren Sornek <karen.sornek@intel.com>
Tested-by: NGurucharan G <gurucharanx.g@intel.com>
Signed-off-by: NTony Nguyen <anthony.l.nguyen@intel.com>