i40e: close client on remove and shutdown

When the driver is removed or shut down, close any attached clients
(i.e. i40iw). This prevents a panic seen sometimes on forced driver
removal or system shutdown when iWarp is running.

Change-ID: I4f6161e5a73ffbb2fd5883567b007310302bfcb5
Signed-off-by: Mitch Williams <mitch.a.williams@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>