i40evf: fix multiple crashes on remove

Depending upon the state of the driver, there are several potential
pitfalls on remove. Kill the watchdog task so rmmod doesn't hang.
Check the adapter->msix_entries field, not the num_msix_vectors field,
which is never cleared.

Change-ID: I0546048477f09fc19e481bd37efa30daae4faa88
Signed-off-by: Mitch Williams <mitch.a.williams@intel.com>
Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Tested-by: Sibai Li <sibai.li@intel.com>
Signed-off-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>