e1000e: add rtnl_lock() to e1000_reset_task

A possible race condition was found in e1000_reset_task,
after discovering a similar issue in igb driver via
commit 024a816 ("igb: reinit_locked() should be called
with rtnl_lock").

Added rtnl_lock() and rtnl_unlock() to avoid this.

Fixes: bc7f75f ("[E1000E]: New pci-express e1000 driver (currently for ICH9 devices only)")
Suggested-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Vitaly Lifshits <vitaly.lifshits@intel.com>
Tested-by: Dvora Fuxbrumer <dvorax.fuxbrumer@linux.intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>

drivers/net/ethernet/intel/e1000e/netdev.c

@@ -5974,15 +5974,19 @@ static void e1000_reset_task(struct work_struct *work)
 	struct e1000_adapter *adapter;
 	adapter = container_of(work, struct e1000_adapter, reset_task);
 
+	rtnl_lock();
 	/* don't run the task if already down */
-	if (test_bit(__E1000_DOWN, &adapter->state))
+	if (test_bit(__E1000_DOWN, &adapter->state)) {
+		rtnl_unlock();
 		return;
+	}
 
 	if (!(adapter->flags & FLAG_RESTART_NOW)) {
 		e1000e_dump(adapter);
 		e_err("Reset adapter unexpectedly\n");
 	}
 	e1000e_reinit_locked(adapter);
+	rtnl_unlock();
 }
 
 /**