i40evf: delay releasing rings

When the VF interface is closed, we cannot immediately free our rings
and RX buffers, because the hardware hasn't yet stopped accessing this
memory. This shows up as a panic or memory corruption when the device is
brought down while under heavy stress.

To fix this, delay releasing resources until we receive acknowledgment
from the PF driver that the rings have indeed been stopped. Because of
this delay, we also need to check to make sure that all of our admin
queue requests have been handled before allowing the device to be
opened.

Change-ID: I44edd35529ce2fa2a9512437a3a8e6f14ed8ed63
Signed-off-by: Mitch Williams <mitch.a.williams@intel.com>
Tested-by: Jim Young <james.m.young@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>