i40e: Fix removing driver while bare-metal VFs pass traffic

Prevent VFs from resetting when PF driver is being unloaded:
- introduce new pf state: __I40E_VF_RESETS_DISABLED;
- check if pf state has __I40E_VF_RESETS_DISABLED state set,
  if so, disable any further VFLR event notifications;
- when i40e_remove (rmmod i40e) is called, disable any resets on
  the VFs;

Previously if there were bare-metal VFs passing traffic and PF
driver was removed, there was a possibility of VFs triggering a Tx
timeout right before iavf_remove. This was causing iavf_close to
not be called because there is a check in the beginning of  iavf_remove
that bails out early if adapter->state < IAVF_DOWN_PENDING. This
makes it so some resources do not get cleaned up.

Fixes: 6a9ddb36

 ("i40e: disable IOV before freeing resources")
Signed-off-by: Slawomir Laba <slawomirx.laba@intel.com>
Signed-off-by: Brett Creeley <brett.creeley@intel.com>
Signed-off-by: Sylwester Dziedziuch <sylwesterx.dziedziuch@intel.com>
Tested-by: Konrad Jankowski <konrad0.jankowski@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>
Link: https://lore.kernel.org/r/20201120180640.3654474-1-anthony.l.nguyen@intel.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>