ixgbevf: Fix rcu warnings induced by LER

Resolve some rcu warnings produced when LER actions take place.
This appears to be due to not holding the rtnl lock when calling
ixgbe_down, so hold the lock. Also avoid disabling the device
when it is already disabled. This check is necessary because the
callback can be called more than once in some cases.

Signed-off-by: Mark Rustad <mark.d.rustad@intel.com>
Tested-by: Phil Schmitt <phillip.j.schmitt@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

drivers/net/ethernet/intel/ixgbevf/ixgbevf.h

@@ -419,6 +419,7 @@ enum ixbgevf_state_t {
 	__IXGBEVF_TESTING,
 	__IXGBEVF_RESETTING,
 	__IXGBEVF_DOWN,
+	__IXGBEVF_DISABLED,
 	__IXGBEVF_REMOVING,
 };