fm10k: no need to continue in fm10k_down if __FM10K_DOWN already set

Return early from fm10k_down() when we are already down, since that
means another thread is either already finished or has started going
down, so shouldn't conflict with them.
Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Tested-by: Krishneil Singh <Krishneil.k.singh@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

drivers/net/ethernet/intel/fm10k/fm10k_pci.c

@@ -1601,7 +1601,8 @@ void fm10k_down(struct fm10k_intfc *interface)
 	int err;
 
 	/* signal that we are down to the interrupt handler and service task */
-	set_bit(__FM10K_DOWN, &interface->state);
+	if (test_and_set_bit(__FM10K_DOWN, &interface->state))
+		return;
 
 	/* call carrier off first to avoid false dev_watchdog timeouts */
 	netif_carrier_off(netdev);